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[FFmpeg-devel] avformat: Add parityfec and ulpfec protocol

Message ID 20210409140750.163086-1-camille@sound4.biz
State New
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Series [FFmpeg-devel] avformat: Add parityfec and ulpfec protocol
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Camille Gonnet April 9, 2021, 2:07 p.m. UTC
Parityfec (RFC 2733) and ulpfec (RFC 5109) generic FEC encoding for RTP streams.

Signed-off-by: Camille Gonnet <camille@sound4.biz>
---
 Changelog                 |   1 +
 doc/general_contents.texi |   1 +
 doc/protocols.texi        | 106 +++++
 libavformat/Makefile      |   1 +
 libavformat/fecrtp.c      | 884 ++++++++++++++++++++++++++++++++++++++
 libavformat/protocols.c   |   1 +
 libavformat/rtpproto.c    |   2 +-
 7 files changed, 995 insertions(+), 1 deletion(-)
 create mode 100644 libavformat/fecrtp.c

Comments

Camille Gonnet April 21, 2021, 7:38 a.m. UTC | #1
I did not have any feedback on this patch.
Thanks,

On April 9, 2021 at 4:08 PM, Camille Gonnet (camille@sound4.biz) wrote:
Parityfec (RFC 2733) and ulpfec (RFC 5109) generic FEC encoding for RTP streams.

Signed-off-by: Camille Gonnet <camille@sound4.biz>
---
 Changelog                 |   1 +
 doc/general_contents.texi |   1 +
 doc/protocols.texi        | 106 +++++
 libavformat/Makefile      |   1 +
 libavformat/fecrtp.c      | 884 ++++++++++++++++++++++++++++++++++++++
 libavformat/protocols.c   |   1 +
 libavformat/rtpproto.c    |   2 +-
 7 files changed, 995 insertions(+), 1 deletion(-)
 create mode 100644 libavformat/fecrtp.c

diff --git a/Changelog b/Changelog
index a96e350e09..e83ec2c60d 100644
--- a/Changelog
+++ b/Changelog
@@ -83,6 +83,7 @@ version <next>:
 - msad video filter
 - gophers protocol
 - RIST protocol via librist
+- FEC RTP (RFC5109+RFC2733) protocol (encoding only)
 
 
 version 4.3:
diff --git a/doc/general_contents.texi b/doc/general_contents.texi
index 33ece6e884..2b70dfb2ad 100644
--- a/doc/general_contents.texi
+++ b/doc/general_contents.texi
@@ -1368,6 +1368,7 @@ performance on systems without hardware floating point support).
 @multitable @columnfractions .4 .1
 @item Name         @tab Support
 @item AMQP         @tab E
+@item FECRTP       @tab X
 @item file         @tab X
 @item FTP          @tab X
 @item Gopher       @tab X
diff --git a/doc/protocols.texi b/doc/protocols.texi
index d3f6cbefcf..403e7b415d 100644
--- a/doc/protocols.texi
+++ b/doc/protocols.texi
@@ -243,6 +243,112 @@ For example, to convert a GIF file given inline with @command{ffmpeg}:
 ffmpeg -i "data:image/gif;base64,R0lGODdhCAAIAMIEAAAAAAAA//8AAP//AP///////////////ywAAAAACAAIAAADF0gEDLojDgdGiJdJqUX02iB4E8Q9jUMkADs=" smiley.png
 @end example
 
+@section fecrtp
+
+FEC for RTP Protocol. Supports ULP FEC (RFC 5109) and Parity FEC (RFC 2733)
+
+The FEC is a generic parity-check forward error correction mechanism
+for RTP Streams.
+
+This protocol must be used in conjunction with the @code{rtp} protocol.
+
+The required syntax is:
+@example
+-fec fecrtp=@var{option}=@var{val}... rtp://@var{hostname}:@var{port}
+@end example
+
+This protocol accepts the following options:
+@table @option
+
+@item payload_type=@var{n}
+Specify RTP payload type for FEC packets (0-127).
+Default value is 98.
+
+@item port=@var{n}
+Specify RTP port for FEC packets (0-127).
+Default value is (RTP port + 2).
+
+@item host=@var{destination}
+Specify RTP destination for FEC packets.
+If not provided, use same as RTP.
+
+@item kind=@var{kind}
+Set the kind of FEC to use. Default is @code{ulpfec}
+Accepts the following options:
+@table @samp
+@item parityfec
+parityfec (RFC 2733)
+@item ulpfec
+ulpfec (RFC 5109)
+@end table
+
+@item length=@var{n}
+Length of recovery, or 0 for full. (0-1472)
+For @code{kind=ulpfec} only.
+Default value is 0 (full).
+
+@item algorithm=@var{algorithm}
+Set the covered packets algorithm. Default is @code{simple}
+Accepts the following options:
+@table @samp
+@item simple
+Simple usage using @code{span},@code{every} and @code{delay},
+@item rotate
+Combine @code{span-1} packets in the last @code{span} packets in every way.@*
+With span=4 and packets a,b,c,d, will produce (a,b,c) (a,b,d) (a,c,d) (b,c,d).
+@item 1d
+Put the packets in a matrix and compute columns FEC (similar to ProMPEG).
+Use @code{col} and @code{row}.
+@end table
+
+@item span=@var{n}
+The number of RTP packets covered by each FEC packet.
+For @code{algorithm=simple} and @code{algorithm=rotate}.
+Default value is 2.
+
+@item every=@var{n}
+How often we add a FEC packet after a RTP packet (1-20).
+This must be a divider of span.
+For @code{algorithm=simple}.
+Default value is 2.
+
+@item delay=@var{n}
+How many RTP packet we should delay the sending of our FEC packet
+when it is ready (0-20)
+For @code{algorithm=simple}.
+Default value is 0.
+
+@item col=@var{n}
+Number of columns in the matrix.
+For @code{algorithm=1d}.
+Default value is 4.
+
+@item row=@var{n}
+Number of rows in the matrix.
+For @code{algorithm=1d}.
+Default value is 4.
+
+@end table
+
+Example usage:
+@itemize @bullet
+@item
+For 1/4 recovery, 25% overhead
+@example
+-fec fecrtp=span=4:every=4 rtp://@var{hostname}:@var{port}
+@end example
+@item
+For 1/10 recovery, 10% overhead in ulpfec
+@example
+-fec fecrtp=kind=ulpfec,span=10:every=10 rtp://@var{hostname}:@var{port}
+@end example
+@item
+For 1d fec with 4 rows and 4 columns
+@example
+-fec fecrtp=algorithm=1d:col=4:row=4 rtp://@var{hostname}:@var{port}
+@end example
+@end itemize
+
 @section file
 
 File access protocol.
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 0f340f74a0..f393ce14ca 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -618,6 +618,7 @@ OBJS-$(CONFIG_CRYPTO_PROTOCOL)           += crypto.o
 OBJS-$(CONFIG_DATA_PROTOCOL)             += data_uri.o
 OBJS-$(CONFIG_FFRTMPCRYPT_PROTOCOL)      += rtmpcrypt.o rtmpdigest.o rtmpdh.o
 OBJS-$(CONFIG_FFRTMPHTTP_PROTOCOL)       += rtmphttp.o
+OBJS-$(CONFIG_FECRTP_PROTOCOL)           += fecrtp.o
 OBJS-$(CONFIG_FILE_PROTOCOL)             += file.o
 OBJS-$(CONFIG_FTP_PROTOCOL)              += ftp.o urldecode.o
 OBJS-$(CONFIG_GOPHER_PROTOCOL)           += gopher.o
diff --git a/libavformat/fecrtp.c b/libavformat/fecrtp.c
new file mode 100644
index 0000000000..7e4de1b267
--- /dev/null
+++ b/libavformat/fecrtp.c
@@ -0,0 +1,884 @@
+/*
+ * FEC for RTP - RFC 5109 and RFC 2733
+ * Copyright (c) 2021 SOUND4, France (http://www.sound4.com)
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * FEC for RTP - RFC 5109 and RFC 2733
+ * @author Camille Gonnet <camille@sound4.biz>
+ */
+
+/*
+ * Note: see also prompeg.c which use a derivative of the RFC 2733.
+ *
+ * Algorithm:
+ * Those FEC compute parity of previous RTP frames, but choice of frame is open.
+ * Here 3 algorithm can be used:
+ *   + Simple
+ *     Uses 3 parameters: span, every and delay
+ *     It computes the parity of 'span' sequential packets and output a FEC packet
+ *     every 'every' RTP packets, delaying the send by 'delay' packets when all
+ *     have been send.
+ *   + Rotate
+ *     Uses 1 parameter: span
+ *     It computes parity of 'span'-1 packets over the last 'span' packets, by
+ *     rotating the missing packet in every way.
+ *     With span=4 and packets a,b,c,d, will produce (a,b,c) (a,b,d) (a,c,d) (b,c,d).
+ *   + 1d
+ *     Uses 2 parameters: col,row
+ *     Put the packets in a matrix and compute columns FEC (similar to ProMPEG)
+ *
+ * A typical set is for instance :
+ *   span=5, every=5, delay=0
+ *     which recovers one packet loss over 5 packets with 20% overhead and 5 delay.
+ *
+ * Reminder:
+
+ [RFC 3550] RTP header
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |V=2|P|X|  CC   |M|     PT      |       sequence number         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                           timestamp                           |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |           synchronization source (SSRC) identifier             |
+   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+   |            contributing source (CSRC) identifiers              |
+   |                             ....                              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 2733] FEC Packet Structure
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                         RTP Header                            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                         FEC Header                            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                         FEC Payload                           |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 2733] Parity Header Format
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |      SN base                  |        length recovery        |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |E| PT recovery |                 mask                          |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                          TS recovery                          |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 5109] FEC Packet Structure
+
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                RTP Header (12 octets or more)                 |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                    FEC Header (10 octets)                     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                      FEC Level 0 Header                       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                     FEC Level 0 Payload                       |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                      FEC Level 1 Header                       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                     FEC Level 1 Payload                       |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                            Cont.                              |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 5109] FEC Header Format
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |E|L|P|X|  CC   |M| PT recovery |            SN base            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                          TS recovery                          |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |        length recovery        |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+
+ [RFC 5109] ULP Level Header Format
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |       Protection Length       |             mask              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |              mask cont. (present only when L = 1)             |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+  */
+
+#include "libavutil/avstring.h"
+#include "libavutil/intreadwrite.h"
+#include "libavutil/opt.h"
+#include "libavutil/parseutils.h"
+#include "libavutil/random_seed.h"
+#include "avformat.h"
+#include "config.h"
+#include "url.h"
+
+typedef struct Fecrtp {
+    uint16_t sn;
+    uint32_t ssrc;
+    uint16_t length_recovery;
+    int size;           // size of the bitstring, so the bigger input packet size
+    uint8_t *bitstring; // We will store the xor of the full packets including RTP header.
+} Fecrtp;
+
+enum {
+    FECRTP_5109                   = 1,
+    FECRTP_2733                   = 2,
+};
+enum {
+    FECRTP_ALGO_SIMPLE            = 1,
+    FECRTP_ALGO_1D                = 2,
+    FECRTP_ALGO_ROTATE            = 3,
+};
+typedef struct FecrtpContext {
+    const AVClass *class;
+
+    int kind;
+    int algorithm;
+
+    int ttl;
+    uint8_t pt;
+    const char *host;
+    uint8_t port;
+    int span, every, delay;
+    int protection_length;
+    int col, row;
+
+    int mask_length;    // in bits
+    int long_header;    // if mask_length>16 (L==1) RFC5109 only
+    URLContext *fec_hd;
+    int fec_arr_len;
+    uint64_t mask;
+
+    Fecrtp **fec_arr;
+    uint8_t *rtp_buf;
+    uint16_t rtp_sn;
+    int packet_idx, packet_idx_max;
+    int bitstring_size;
+    int rtp_buf_size;
+    int init;
+    int first;
+    int last_idx;
+} FecrtpContext;
+
+#define OFFSET(x) offsetof(FecrtpContext, x)
+#define E AV_OPT_FLAG_ENCODING_PARAM
+
+static const AVOption options[] = {
+    { "ttl",   "Time to live (in milliseconds, multicast only)", OFFSET(ttl),
+        AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, .flags = E },
+    { "payload_type", "Specify RTP payload type for FEC packets", OFFSET(pt),
+        AV_OPT_TYPE_INT, { .i64 = 98 }, 0, 127, .flags = E },
+    { "port", "Specify RTP port. Default is RTP port + 2", OFFSET(port),
+        AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 127, .flags = E },
+    { "host", "Specify destination host. Default is same as RTP", OFFSET(host),
+        AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, .flags = E },
+    { "kind", "Set the FEC kind",
+      OFFSET(kind), AV_OPT_TYPE_INT, { .i64 = FECRTP_5109 }, 1, 2, E, "kind" },
+        { "parityfec", "parityfec (RFC 2733)",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_2733 }, 1, 2, E, "kind" },
+        { "ulpfec", "ulpfec (RFC 5109)",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_5109 }, 1, 2, E, "kind" },
+    { "algorithm", "Set the covered packets algorithm",
+      OFFSET(algorithm), AV_OPT_TYPE_INT, { .i64 = FECRTP_ALGO_SIMPLE }, 1, 3, E, "algorithm" },
+        { "simple", "Simple: use span/every/delay",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_ALGO_SIMPLE }, 1, 3, E, "algorithm" },
+        { "rotate", "Rotating: combine (span-1) packets in the last (span) packets in every way.",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_ALGO_ROTATE }, 1, 3, E, "algorithm" },
+        { "1d", "1D: column mode (similar to ST2022-1). Use col/row",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_ALGO_1D }, 1, 3, E, "algorithm" },
+    { "span",  "Number of packets covered each time (algorithm=simple,rotate)", OFFSET(span),
+        AV_OPT_TYPE_INT, { .i64 =  2 }, 2, 24, .flags = E },
+    { "every", "Insert a FEC packet every # RTP packets (algorithm=simple)", OFFSET(every),
+        AV_OPT_TYPE_INT, { .i64 =  2 }, 1, 24, .flags = E },
+    { "delay", "Send FEC packet # packets after last covered (algorithm=simple)", OFFSET(delay),
+        AV_OPT_TYPE_INT, { .i64 =  0 }, 0, 24, .flags = E },
+    { "col", "Number of matrix column (algorithm=1d)", OFFSET(col),
+        AV_OPT_TYPE_INT, { .i64 =  4 }, 2, 24, .flags = E },
+    { "row", "Number of matrix row (algorithm=1d)", OFFSET(row),
+        AV_OPT_TYPE_INT, { .i64 =  4 }, 2, 24, .flags = E },
+
+    { NULL }
+};
+
+static const AVClass fecrtp_class = {
+    .class_name = "fecrtp",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
+static void xor_fast(const uint8_t *in1, int size1, const uint8_t *in2, int size2, uint8_t *out, int size) {
+    int i, n, s, sizemin;
+#if HAVE_FAST_64BIT
+    uint64_t v1, v2;
+#else
+    uint32_t v1, v2;
+#endif
+
+    size = FFMAX(size1, size2);
+    sizemin = FFMIN(size1, size2);
+
+    // Do the XOR where both have data
+#if HAVE_FAST_64BIT
+    n = sizemin / sizeof (uint64_t);
+    s = n * sizeof (uint64_t);
+
+    for (i = 0; i < n; i++) {
+        v1 = AV_RN64A(in1);
+        v2 = AV_RN64A(in2);
+        AV_WN64A(out, v1 ^ v2);
+        in1 += 8;
+        in2 += 8;
+        out += 8;
+    }
+#else
+    n = sizemin / sizeof (uint32_t);
+    s = n * sizeof (uint32_t);
+
+    for (i = 0; i < n; i++) {
+        v1 = AV_RN32A(in1);
+        v2 = AV_RN32A(in2);
+        AV_WN32A(out, v1 ^ v2);
+        in1 += 4;
+        in2 += 4;
+        out += 4;
+    }
+#endif
+
+    n = sizemin - s;
+
+    for (i = 0; i < n; i++) {
+        out[i] = in1[i] ^ in2[i];
+    }
+    s += n;
+
+    // Compute the part where only one has data (padding 0)
+    n = size - s;
+    if (n > 0) {
+        if (size1 >= size2) {
+            memcpy(out,in1, n);
+        } else {
+            memcpy(out,in2, n);
+        }
+    }
+}
+
+static uint16_t bitrev16(uint16_t x)
+{
+       x = (((x & 0xaaaa) >> 1) | ((x & 0x5555) << 1));
+       x = (((x & 0xcccc) >> 2) | ((x & 0x3333) << 2));
+       x = (((x & 0xf0f0) >> 4) | ((x & 0x0f0f) << 4));
+       return((x >> 8) | (x << 8));
+}
+
+static uint32_t bitrev32(uint32_t x)
+{
+       x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1));
+       x = (((x & 0xcccccccc) >> 2) | ((x & 0x33333333) << 2));
+       x = (((x & 0xf0f0f0f0) >> 4) | ((x & 0x0f0f0f0f) << 4));
+       x = (((x & 0xff00ff00) >> 8) | ((x & 0x00ff00ff) << 8));
+    return((x >> 16) | (x << 16));
+}
+
+static int fecrtp_init_fecpacket(URLContext *h, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+    int idx;
+
+    s->last_idx++;
+    if (s->last_idx == s->fec_arr_len)
+        s->last_idx = 0;
+    idx = s->last_idx;
+
+    // sanity check only, should not happen if algorithm are handled properly.
+    if (s->fec_arr[idx]->size>0) {
+        av_log(h, AV_LOG_ERROR, "Internal error, buffer already used (%d)\n", idx);
+        return AVERROR(EINVAL);
+    }
+
+    s->fec_arr[idx]->sn = AV_RB16(buf + 2);
+    // The SSRC value will generally be the same as the SSRC value of the media stream it protects
+    // It MAY be different if the FEC stream is being demultiplexed via the SSRC
+    s->fec_arr[idx]->ssrc = AV_RB32(buf + 8);
+    // Initialize it with the content
+    memcpy(s->fec_arr[idx]->bitstring, buf, size);
+    s->fec_arr[idx]->size = size;
+    s->fec_arr[idx]->length_recovery = (size-12);
+
+    //av_log(h, AV_LOG_DEBUG, "Starting new FEC[%d] SN=%hu SSRC=%X size=%d (packet idx %d)\n",
+        //idx, s->fec_arr[idx]->sn, s->fec_arr[idx]->ssrc, s->fec_arr[idx]->size, s->packet_idx);
+    return 0;
+}
+
+static int fecrtp_add_fecpacket(URLContext *h, int idx, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+
+    if (s->fec_arr[idx]->size>0) {
+        //av_log(h, AV_LOG_DEBUG, "Adding to FEC[%d] (packet idx %d)\n", idx, s->packet_idx);
+
+        xor_fast(s->fec_arr[idx]->bitstring, s->fec_arr[idx]->size,
+            buf, size,
+            s->fec_arr[idx]->bitstring, FFMAX(size, s->fec_arr[idx]->size));
+        s->fec_arr[idx]->length_recovery ^= (size-12);
+        if (s->fec_arr[idx]->size < size) {
+            s->fec_arr[idx]->size = size;
+        }
+    }
+    return 0;
+}
+
+static int fecrtp_write_fec2733(URLContext *h, Fecrtp *fec, uint32_t ts_current, uint64_t mask) {
+    FecrtpContext *s = h->priv_data;
+    uint8_t *buf = s->rtp_buf; // zero-filled
+    uint8_t *b = fec->bitstring;
+    uint16_t sn;
+    int ret;
+
+    sn = ++s->rtp_sn;
+
+    // RTP Header (12 bytes)
+    // V=2, P=xor, X=xor, CC=xor
+    buf[0] = 0x80| (b[0] & 0x3f);
+    // M=xor, PT=fixed
+    buf[1] = (b[1] & 0x80) | s->pt;
+    // SN=ours
+    AV_WB16(buf + 2, sn);
+    // TS=current
+    AV_WB32(buf + 4, ts_current);
+    // SSRC=original
+    AV_WB32(buf + 8, fec->ssrc);
+    // no CSRC or extension, even if bits X or E are set.
+
+    // FEC Header (12 bytes)
+    // SN:original first
+    AV_WB16(buf + 12, fec->sn);
+    // length recovery:xor
+    AV_WB16(buf + 14, fec->length_recovery);
+    // E=0, PT=xor
+    buf[16]=(b[1] & 0X7f);
+    // MASK:MASK (MSb First)
+    AV_WB24(buf + 17, mask);
+    // TS:xor
+    memcpy(buf + 20, b + 4, 4);
+
+    // Payload : part after basic RTP header (12 bytes) of all frames
+    memcpy(buf + 24, b + 12, fec->size-12);
+
+    ret = ffurl_write(s->fec_hd, buf, 24 + fec->size - 12);
+    return ret;
+}
+
+static int fecrtp_write_fec5109(URLContext *h, Fecrtp *fec, uint32_t ts_current, uint64_t mask) {
+    FecrtpContext *s = h->priv_data;
+    uint8_t *buf = s->rtp_buf; // zero-filled
+    uint8_t *b = fec->bitstring;
+    uint16_t sn;
+    int ret;
+    int headerlen;
+
+    sn = ++s->rtp_sn;
+
+    // RTP Header (12 bytes)
+    // V=2, P=0, X=0, CC=0
+    buf[0] = 0x80;
+    // M=0, PT=fixed
+    buf[1] = s->pt;
+    // SN=ours
+    AV_WB16(buf + 2, sn);
+    // TS=current
+    AV_WB32(buf + 4, ts_current);
+    // SSRC=original
+    AV_WB32(buf + 8, fec->ssrc);
+    // no CSRC
+
+    // FEC Header (10 bytes)
+    // E=0, L=0|1, P,X,CC:xor
+    buf[12] = (s->long_header<<6) | (b[0] & 0x3F);
+    // M,PT:xor
+    buf[13] = b[1];
+    // SN:original first
+    AV_WB16(buf + 14, fec->sn);
+    // TS:xor
+    memcpy(buf + 16, b + 4, 4);
+    // length:xor
+    AV_WB16(buf + 20, fec->length_recovery);
+
+    // FEC Level 0 Header
+    // Protection Length: note clear in RFC, guess this is the level payload length
+    AV_WB16(buf + 22, fec->size-12);
+    // Mask : (LSb First)
+    AV_WB16(buf + 24, bitrev16(mask));
+    headerlen = 24+2;
+    if (s->long_header) {
+        mask >>= 16;
+        AV_WB32(buf + 26, bitrev32(mask));
+        headerlen += 4;
+    }
+    // Payload : part after basic RTP header (12 bytes) of all frames
+    memcpy(buf + headerlen, b + 12, fec->size-12);
+
+    ret = ffurl_write(s->fec_hd, buf, headerlen + fec->size - 12);
+    return ret;
+}
+
+static int fecrtp_send_fecpacket(URLContext *h, int idx, const uint8_t *buf, uint64_t mask) {
+    FecrtpContext *s = h->priv_data;
+    uint32_t ts_current;
+    int ret = 0;
+
+    // Sanity check, should not happen if algorithm are handled properly.
+    if (!s->fec_arr[idx]->size) {
+        av_log(h, AV_LOG_ERROR, "Internal error, want to send uninitialized buffer (%d)\n", idx);
+        return AVERROR(EINVAL);
+    }
+
+    // The timestamp MUST be set to the value of the media
+    // RTP clock at the instant the FEC packet is transmitted
+    ts_current = AV_RB32(buf + 4);
+    switch (s->kind) {
+    case FECRTP_2733:
+        if ((ret = fecrtp_write_fec2733(h, s->fec_arr[idx], ts_current, mask)) < 0)
+            goto end;
+        break;
+    case FECRTP_5109:
+        if ((ret = fecrtp_write_fec5109(h, s->fec_arr[idx], ts_current, mask)) < 0)
+            goto end;
+        break;
+    };
+    // mark packet as free for reuse (internal check)
+    s->fec_arr[idx]->size = 0;
+
+end:
+    return ret;
+}
+
+static int fecrtp_open(URLContext *h, const char *uri, int flags) {
+    FecrtpContext *s = h->priv_data;
+    AVDictionary *udp_opts = NULL;
+    int rtp_port, fec_port;
+    char rtp_hostname[256];
+    const char *hostname;
+    char buf[1024];
+
+    s->fec_hd = NULL;
+
+    av_url_split(NULL, 0, NULL, 0, rtp_hostname, sizeof (rtp_hostname), &rtp_port,
+            NULL, 0, uri);
+
+    if (s->port) {
+        fec_port = s->port;
+    } else {
+        if (rtp_port < 1 || rtp_port > UINT16_MAX - 2) {
+            av_log(h, AV_LOG_ERROR, "Invalid RTP base port %d\n", rtp_port);
+            return AVERROR(EINVAL);
+        }
+        fec_port = rtp_port + 2;
+    }
+    if (s->host) {
+        hostname = s->host;
+    } else {
+        hostname = rtp_hostname;
+    }
+
+    if (s->ttl > 0) {
+        av_dict_set_int(&udp_opts, "ttl", s->ttl, 0);
+    }
+
+    ff_url_join(buf, sizeof (buf), "udp", NULL, hostname, fec_port, NULL);
+    if (ffurl_open_whitelist(&s->fec_hd, buf, flags, &h->interrupt_callback,
+            &udp_opts, h->protocol_whitelist, h->protocol_blacklist, h) < 0)
+        goto fail;
+
+    h->max_packet_size = s->fec_hd->max_packet_size;
+    s->init = 1;
+
+    av_dict_free(&udp_opts);
+    return 0;
+
+fail:
+    ffurl_closep(&s->fec_hd);
+    av_dict_free(&udp_opts);
+    return AVERROR(EIO);
+}
+
+static int fecrtp_init(URLContext *h, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+    uint32_t seed;
+    int i;
+    uint64_t mask_bit;
+
+    s->fec_arr = NULL;
+    s->rtp_buf = NULL;
+
+    if (size < 12 || size > UINT16_MAX + 12) {
+        av_log(h, AV_LOG_ERROR, "Invalid RTP packet size\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        if ( (s->span < s->every) || (s->span % s->every)!=0 ) {
+            av_log(h, AV_LOG_ERROR, "'span' must be a multiple of 'every'\n");
+            return AVERROR_INVALIDDATA;
+        }
+        s->mask_length = s->span;
+        break;
+    case FECRTP_ALGO_ROTATE:
+        s->mask_length = s->span - 1;
+        break;
+    case FECRTP_ALGO_1D:
+        s->span = s->row * s->col;
+        s->mask_length = s->row * s->col;
+        break;
+    };
+
+    switch (s->kind) {
+    case FECRTP_2733:
+        if (s->mask_length > 24) {
+            av_log(h, AV_LOG_ERROR, "Invalid FEC parameters: maximum mask is 24 bits\n");
+            return AVERROR_INVALIDDATA;
+        }
+        break;
+    case FECRTP_5109:
+        s->long_header = (s->mask_length > 16)? 1 : 0;
+        if (s->mask_length > 48) {
+            av_log(h, AV_LOG_ERROR, "Invalid FEC parameters: maximum mask is 48 bits\n");
+            return AVERROR_INVALIDDATA;
+        }
+        break;
+    };
+    s->mask=0;
+    mask_bit=1;
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        for (i=0;i<s->span;i++) {
+            s->mask |= mask_bit;
+            mask_bit <<= 1;
+        }
+        s->fec_arr_len = s->span / s->every + s->delay;
+        // Round up packet index to a multiple of fec_arr_len
+        s->packet_idx_max = INT_MAX - (INT_MAX % s->fec_arr_len);
+        break;
+    case FECRTP_ALGO_ROTATE:
+        // mask will change each time, by removing 1 bit
+        s->mask = (1<<s->span) -1;
+        s->fec_arr_len = s->span;
+        // Round up packet index to a multiple of fec_arr_len
+        s->packet_idx_max = INT_MAX - (INT_MAX % s->fec_arr_len);
+        break;
+    case FECRTP_ALGO_1D:
+        for (i=0;i< s->row;i++) {
+            s->mask |= mask_bit;
+            mask_bit <<= s->col;
+        }
+        s->fec_arr_len = s->col * 2;
+        // Round up packet index to a multiple of fec_arr_len
+        s->packet_idx_max = INT_MAX - (INT_MAX % (s->col * s->row));
+        break;
+    };
+
+    s->packet_idx = 0;
+    if (h->flags & AVFMT_FLAG_BITEXACT) {
+        s->rtp_sn = 0;
+    } else {
+        seed = av_get_random_seed();
+        s->rtp_sn = seed & 0x0fff;
+    }
+
+    if (s->kind == FECRTP_2733) {
+        s->rtp_buf_size = 24 + h->max_packet_size; // 12 + 12: RTP + FEC headers
+        s->bitstring_size = 10 + h->max_packet_size; // 10: P, X, CC, M, PT, SN, TS, Length
+    } else /* if (s->kind == FECRTP_5109) */ {
+        s->rtp_buf_size = 28 + (s->protection_length?s->protection_length:h->max_packet_size); // 12 + 16: RTP + FEC headers
+        s->bitstring_size = 10 + (s->protection_length?s->protection_length:h->max_packet_size); // 10: P, X, CC, M, PT, SN, TS, Length
+    }
+
+    s->fec_arr = av_malloc_array(s->fec_arr_len, sizeof (Fecrtp*));
+    if (!s->fec_arr) {
+        goto fail;
+    }
+    for (i = 0; i < s->fec_arr_len; i++) {
+        s->fec_arr[i] = av_malloc(sizeof (Fecrtp));
+        if (!s->fec_arr[i]) {
+            goto fail;
+        }
+        s->fec_arr[i]->size=0;
+        s->fec_arr[i]->bitstring = av_malloc_array(s->bitstring_size, sizeof (uint8_t));
+        if (!s->fec_arr[i]->bitstring) {
+            av_freep(&s->fec_arr[i]);
+            goto fail;
+        }
+    }
+    // Simplifying: first one will be 0 in array
+    s->last_idx = s->fec_arr_len-1;
+
+    s->rtp_buf = av_malloc_array(s->rtp_buf_size, sizeof (uint8_t));
+    if (!s->rtp_buf) {
+        goto fail;
+    }
+    memset(s->rtp_buf, 0, s->rtp_buf_size);
+
+    s->init = 0;
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        s->first = s->span + s->delay - 1;
+        av_log(h, AV_LOG_INFO, "FEC: %s algorithm simple, span=%d every=%d delay=%d\n",
+            s->kind==FECRTP_5109?"ulpfec":"parityfec", s->span, s->every, s->delay);
+        break;
+    case FECRTP_ALGO_ROTATE:
+        s->first = 0;
+        av_log(h, AV_LOG_INFO, "FEC: %s algorithm rotate, span=%d\n",
+            s->kind==FECRTP_5109?"ulpfec":"parityfec", s->span);
+        break;
+    case FECRTP_ALGO_1D:
+        s->first = s->col * s->row;
+        av_log(h, AV_LOG_INFO, "FEC: %s algorithm 1d, col=%d, row=%d\n",
+            s->kind==FECRTP_5109?"ulpfec":"parityfec", s->col, s->row);
+        break;
+    };
+
+    return 0;
+
+fail:
+    av_log(h, AV_LOG_ERROR, "Failed to allocate the FEC buffer\n");
+    return AVERROR(ENOMEM);
+}
+
+static int fecrtp_write(URLContext *h, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+    int idx, first_is_new=0;
+    int ret = 0;
+    int protected_size = size;
+    uint64_t mask_clear;
+    int cur_row, cur_col;
+
+    if (s->kind == FECRTP_5109) {
+        // if protection_length is set, forget all after
+        if (s->protection_length > 0 && protected_size > s->protection_length)
+            protected_size = s->protection_length;
+    }
+
+    if (s->init && ((ret = fecrtp_init(h, buf, protected_size)) < 0))
+        goto end;
+
+    if (protected_size > s->bitstring_size) {
+        av_log(h, AV_LOG_ERROR, "The RTP packet size exceed the max_packet_size\n");
+        return AVERROR(EINVAL);
+    }
+
+    idx = s->last_idx;
+    // Create/Update needed FEC packets
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        if (s->packet_idx % s->every == 0) {
+            if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                goto end;
+
+            // Do not xor this one
+            first_is_new = 1;
+        }
+        // One RTP packet will be used in (span/every) FEC packets
+        for (int n=0; n < s->span/s->every; n++) {
+            if (first_is_new) {
+                first_is_new--;
+            } else {
+                // next one to process
+                if (!idx)
+                    idx = s->fec_arr_len;
+                idx--;
+                if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                    goto end;
+            }
+        }
+        break;
+    case FECRTP_ALGO_ROTATE:
+        // comments for case span==4
+        if (s->packet_idx % s->span == 0) {
+            // create all but last (a,b,c) (a,b,d) (a,c,d)
+            for (int n=0; n < s->span-1; n++) {
+                if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                    goto end;
+            }
+            // idx is on last
+        } else if (s->packet_idx % s->span == 1) {
+            // create last now (b,c,d)
+            if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                goto end;
+            // And XOR all but two last (last just created)
+            for (int n=0; n < s->span-2; n++) {
+                // Add the xor to all but
+                idx=s->last_idx+1+n;
+                if (idx >= s->fec_arr_len)
+                    idx -= s->fec_arr_len;
+                if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                    goto end;
+            }
+            // idx is on last-1
+        } else {
+            // XOR all but last-packet_idx
+            for (int n=0; n < s->span; n++) {
+                idx=s->last_idx+1+n;
+                if (idx >= s->fec_arr_len)
+                    idx -= s->fec_arr_len;
+                if (n != (s->span - 1 - (s->packet_idx % s->span))) {
+                    if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                        goto end;
+                }
+            }
+        }
+        break;
+    case FECRTP_ALGO_1D:
+        // Where are we in matrix
+        cur_col = s->packet_idx % s->col;
+        cur_row = (s->packet_idx / s->col ) % s->row;
+        if (!cur_row) {
+            // First row, we create the FEC at each column
+            if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                goto end;
+        } else {
+            // we process current column
+            idx = (s->last_idx - s->col + 1) + cur_col;
+            if (idx >= s->fec_arr_len)
+                idx -= s->fec_arr_len;
+            if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                goto end;
+        }
+        break;
+    };
+
+    // Send needed FEC packets
+    if (s->first) {
+        // Not enough data to send
+        //av_log(h, AV_LOG_DEBUG, "not sending (first=%d)\n", s->first);
+        s->first--;
+    } else {
+        switch (s->algorithm) {
+        case FECRTP_ALGO_SIMPLE:
+            // Should we send now ?
+            if ((s->packet_idx - (s->span-1) - s->delay) % s->every == 0) {
+                // Skip the delay if needed
+                idx-=s->delay+1;
+                if (idx < 0)
+                    idx += s->fec_arr_len;
+                if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask)) < 0)
+                    goto end;
+            }
+            break;
+        case FECRTP_ALGO_ROTATE:
+            // comments for case span==4
+            if (s->packet_idx % s->span == s->span - 2) {
+                // Send first one at one before last
+                mask_clear=1<<(s->span-1);  // This one is not in the xor
+                idx=s->last_idx+1;  // circular -> go first
+                if (idx >= s->fec_arr_len)
+                    idx -= s->fec_arr_len;
+                if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask & (~mask_clear))) < 0)
+                    goto end;
+            } else if (s->packet_idx % s->span == s->span - 1) {
+                // Send all others on last
+                for (int n=1; n < s->span; n++) {
+                    mask_clear=1<<(s->span-1-n);  // This one is not in the xor
+                    // For the last one, we started one later, so clear MSB
+                    if (n == s->span-1)
+                        mask_clear=1<<(s->span-1);
+                    idx=s->last_idx+1+n;
+                    if (idx >= s->fec_arr_len)
+                        idx -= s->fec_arr_len;
+                    if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask & (~mask_clear))) < 0)
+                        goto end;
+                }
+            }
+            break;
+        case FECRTP_ALGO_1D:
+            // cur_col and cur_row already set to where we are in matrix
+            // evenly space them, starting of 1st of matrix
+            // we have s->col to send in s->col*s->row packets
+            if ((cur_col+cur_row*s->col)%s->row == 0) {
+                // Find index of first of previous matrix
+                if (!cur_row) {
+                    // only cur_col has been added for new matrix
+                    idx = (s->last_idx - cur_col + s->col);
+                } else {
+                    // all have been added  for new matrix
+                    idx = (s->last_idx  + 1);
+                }
+                idx += (cur_col+cur_row*s->col)/s->row;
+                idx %= s->fec_arr_len;
+                if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask)) < 0)
+                    goto end;
+            }
+            break;
+        };
+    }
+
+    // prepare for next packet
+    s->packet_idx++;
+    if (s->packet_idx == s->packet_idx_max)
+        s->packet_idx = 0;
+
+    ret = protected_size;
+
+end:
+    return ret;
+}
+
+static int fecrtp_close(URLContext *h) {
+    FecrtpContext *s = h->priv_data;
+    int i;
+
+    ffurl_closep(&s->fec_hd);
+
+    if (s->fec_arr) {
+        for (i = 0; i < s->fec_arr_len; i++) {
+            av_free(s->fec_arr[i]->bitstring);
+            av_freep(&s->fec_arr[i]);
+        }
+        av_freep(&s->fec_arr);
+    }
+    av_freep(&s->rtp_buf);
+
+    return 0;
+}
+
+const URLProtocol ff_fecrtp_protocol = {
+    .name                      = "fecrtp",
+    .url_open                  = fecrtp_open,
+    .url_write                 = fecrtp_write,
+    .url_close                 = fecrtp_close,
+    .priv_data_size            = sizeof(FecrtpContext),
+    .flags                     = URL_PROTOCOL_FLAG_NETWORK,
+    .priv_data_class           = &fecrtp_class,
+};
diff --git a/libavformat/protocols.c b/libavformat/protocols.c
index fb6fabdce5..af16313fdb 100644
--- a/libavformat/protocols.c
+++ b/libavformat/protocols.c
@@ -31,6 +31,7 @@ extern const URLProtocol ff_crypto_protocol;
 extern const URLProtocol ff_data_protocol;
 extern const URLProtocol ff_ffrtmpcrypt_protocol;
 extern const URLProtocol ff_ffrtmphttp_protocol;
+extern const URLProtocol ff_fecrtp_protocol;
 extern const URLProtocol ff_file_protocol;
 extern const URLProtocol ff_ftp_protocol;
 extern const URLProtocol ff_gopher_protocol;
diff --git a/libavformat/rtpproto.c b/libavformat/rtpproto.c
index 7dd6042158..a58472d684 100644
--- a/libavformat/rtpproto.c
+++ b/libavformat/rtpproto.c
@@ -295,7 +295,7 @@ static int rtp_open(URLContext *h, const char *uri, int flags)
             av_log(h, AV_LOG_ERROR, "Failed to parse the FEC protocol value\n");
             goto fail;
         }
-        if (strcmp(fec_protocol, "prompeg")) {
+        if (strcmp(fec_protocol, "prompeg") && strcmp(fec_protocol, "fecrtp")) {
             av_log(h, AV_LOG_ERROR, "Unsupported FEC protocol %s\n", fec_protocol);
             goto fail;
         }
--
2.25.1
diff mbox series

Patch

diff --git a/Changelog b/Changelog
index a96e350e09..e83ec2c60d 100644
--- a/Changelog
+++ b/Changelog
@@ -83,6 +83,7 @@  version <next>:
 - msad video filter
 - gophers protocol
 - RIST protocol via librist
+- FEC RTP (RFC5109+RFC2733) protocol (encoding only)
 
 
 version 4.3:
diff --git a/doc/general_contents.texi b/doc/general_contents.texi
index 33ece6e884..2b70dfb2ad 100644
--- a/doc/general_contents.texi
+++ b/doc/general_contents.texi
@@ -1368,6 +1368,7 @@  performance on systems without hardware floating point support).
 @multitable @columnfractions .4 .1
 @item Name         @tab Support
 @item AMQP         @tab E
+@item FECRTP       @tab X
 @item file         @tab X
 @item FTP          @tab X
 @item Gopher       @tab X
diff --git a/doc/protocols.texi b/doc/protocols.texi
index d3f6cbefcf..403e7b415d 100644
--- a/doc/protocols.texi
+++ b/doc/protocols.texi
@@ -243,6 +243,112 @@  For example, to convert a GIF file given inline with @command{ffmpeg}:
 ffmpeg -i "data:image/gif;base64,R0lGODdhCAAIAMIEAAAAAAAA//8AAP//AP///////////////ywAAAAACAAIAAADF0gEDLojDgdGiJdJqUX02iB4E8Q9jUMkADs=" smiley.png
 @end example
 
+@section fecrtp
+
+FEC for RTP Protocol. Supports ULP FEC (RFC 5109) and Parity FEC (RFC 2733)
+
+The FEC is a generic parity-check forward error correction mechanism
+for RTP Streams.
+
+This protocol must be used in conjunction with the @code{rtp} protocol.
+
+The required syntax is:
+@example
+-fec fecrtp=@var{option}=@var{val}... rtp://@var{hostname}:@var{port}
+@end example
+
+This protocol accepts the following options:
+@table @option
+
+@item payload_type=@var{n}
+Specify RTP payload type for FEC packets (0-127).
+Default value is 98.
+
+@item port=@var{n}
+Specify RTP port for FEC packets (0-127).
+Default value is (RTP port + 2).
+
+@item host=@var{destination}
+Specify RTP destination for FEC packets.
+If not provided, use same as RTP.
+
+@item kind=@var{kind}
+Set the kind of FEC to use. Default is @code{ulpfec}
+Accepts the following options:
+@table @samp
+@item parityfec
+parityfec (RFC 2733)
+@item ulpfec
+ulpfec (RFC 5109)
+@end table
+
+@item length=@var{n}
+Length of recovery, or 0 for full. (0-1472)
+For @code{kind=ulpfec} only.
+Default value is 0 (full).
+
+@item algorithm=@var{algorithm}
+Set the covered packets algorithm. Default is @code{simple}
+Accepts the following options:
+@table @samp
+@item simple
+Simple usage using @code{span},@code{every} and @code{delay},
+@item rotate
+Combine @code{span-1} packets in the last @code{span} packets in every way.@*
+With span=4 and packets a,b,c,d, will produce (a,b,c) (a,b,d) (a,c,d) (b,c,d).
+@item 1d
+Put the packets in a matrix and compute columns FEC (similar to ProMPEG).
+Use @code{col} and @code{row}.
+@end table
+
+@item span=@var{n}
+The number of RTP packets covered by each FEC packet.
+For @code{algorithm=simple} and @code{algorithm=rotate}.
+Default value is 2.
+
+@item every=@var{n}
+How often we add a FEC packet after a RTP packet (1-20).
+This must be a divider of span.
+For @code{algorithm=simple}.
+Default value is 2.
+
+@item delay=@var{n}
+How many RTP packet we should delay the sending of our FEC packet
+when it is ready (0-20)
+For @code{algorithm=simple}.
+Default value is 0.
+
+@item col=@var{n}
+Number of columns in the matrix.
+For @code{algorithm=1d}.
+Default value is 4.
+
+@item row=@var{n}
+Number of rows in the matrix.
+For @code{algorithm=1d}.
+Default value is 4.
+
+@end table
+
+Example usage:
+@itemize @bullet
+@item
+For 1/4 recovery, 25% overhead
+@example
+-fec fecrtp=span=4:every=4 rtp://@var{hostname}:@var{port}
+@end example
+@item
+For 1/10 recovery, 10% overhead in ulpfec
+@example
+-fec fecrtp=kind=ulpfec,span=10:every=10 rtp://@var{hostname}:@var{port}
+@end example
+@item
+For 1d fec with 4 rows and 4 columns
+@example
+-fec fecrtp=algorithm=1d:col=4:row=4 rtp://@var{hostname}:@var{port}
+@end example
+@end itemize
+
 @section file
 
 File access protocol.
diff --git a/libavformat/Makefile b/libavformat/Makefile
index 0f340f74a0..f393ce14ca 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -618,6 +618,7 @@  OBJS-$(CONFIG_CRYPTO_PROTOCOL)           += crypto.o
 OBJS-$(CONFIG_DATA_PROTOCOL)             += data_uri.o
 OBJS-$(CONFIG_FFRTMPCRYPT_PROTOCOL)      += rtmpcrypt.o rtmpdigest.o rtmpdh.o
 OBJS-$(CONFIG_FFRTMPHTTP_PROTOCOL)       += rtmphttp.o
+OBJS-$(CONFIG_FECRTP_PROTOCOL)           += fecrtp.o
 OBJS-$(CONFIG_FILE_PROTOCOL)             += file.o
 OBJS-$(CONFIG_FTP_PROTOCOL)              += ftp.o urldecode.o
 OBJS-$(CONFIG_GOPHER_PROTOCOL)           += gopher.o
diff --git a/libavformat/fecrtp.c b/libavformat/fecrtp.c
new file mode 100644
index 0000000000..7e4de1b267
--- /dev/null
+++ b/libavformat/fecrtp.c
@@ -0,0 +1,884 @@ 
+/*
+ * FEC for RTP - RFC 5109 and RFC 2733
+ * Copyright (c) 2021 SOUND4, France (http://www.sound4.com)
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * FEC for RTP - RFC 5109 and RFC 2733
+ * @author Camille Gonnet <camille@sound4.biz>
+ */
+
+/*
+ * Note: see also prompeg.c which use a derivative of the RFC 2733.
+ *
+ * Algorithm:
+ * Those FEC compute parity of previous RTP frames, but choice of frame is open.
+ * Here 3 algorithm can be used:
+ *   + Simple
+ *     Uses 3 parameters: span, every and delay
+ *     It computes the parity of 'span' sequential packets and output a FEC packet
+ *     every 'every' RTP packets, delaying the send by 'delay' packets when all
+ *     have been send.
+ *   + Rotate
+ *     Uses 1 parameter: span
+ *     It computes parity of 'span'-1 packets over the last 'span' packets, by
+ *     rotating the missing packet in every way.
+ *     With span=4 and packets a,b,c,d, will produce (a,b,c) (a,b,d) (a,c,d) (b,c,d).
+ *   + 1d
+ *     Uses 2 parameters: col,row
+ *     Put the packets in a matrix and compute columns FEC (similar to ProMPEG)
+ *
+ * A typical set is for instance :
+ *   span=5, every=5, delay=0
+ *     which recovers one packet loss over 5 packets with 20% overhead and 5 delay.
+ *
+ * Reminder:
+
+ [RFC 3550] RTP header
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |V=2|P|X|  CC   |M|     PT      |       sequence number         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                           timestamp                           |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |           synchronization source (SSRC) identifier             |
+   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
+   |            contributing source (CSRC) identifiers              |
+   |                             ....                              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 2733] FEC Packet Structure
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                         RTP Header                            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                         FEC Header                            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                         FEC Payload                           |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 2733] Parity Header Format
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |      SN base                  |        length recovery        |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |E| PT recovery |                 mask                          |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                          TS recovery                          |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 5109] FEC Packet Structure
+
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                RTP Header (12 octets or more)                 |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                    FEC Header (10 octets)                     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                      FEC Level 0 Header                       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                     FEC Level 0 Payload                       |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                      FEC Level 1 Header                       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                     FEC Level 1 Payload                       |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                            Cont.                              |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ [RFC 5109] FEC Header Format
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |E|L|P|X|  CC   |M| PT recovery |            SN base            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                          TS recovery                          |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |        length recovery        |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+
+ [RFC 5109] ULP Level Header Format
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |       Protection Length       |             mask              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |              mask cont. (present only when L = 1)             |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+  */
+
+#include "libavutil/avstring.h"
+#include "libavutil/intreadwrite.h"
+#include "libavutil/opt.h"
+#include "libavutil/parseutils.h"
+#include "libavutil/random_seed.h"
+#include "avformat.h"
+#include "config.h"
+#include "url.h"
+
+typedef struct Fecrtp {
+    uint16_t sn;
+    uint32_t ssrc;
+    uint16_t length_recovery;
+    int size;           // size of the bitstring, so the bigger input packet size
+    uint8_t *bitstring; // We will store the xor of the full packets including RTP header.
+} Fecrtp;
+
+enum {
+    FECRTP_5109                   = 1,
+    FECRTP_2733                   = 2,
+};
+enum {
+    FECRTP_ALGO_SIMPLE            = 1,
+    FECRTP_ALGO_1D                = 2,
+    FECRTP_ALGO_ROTATE            = 3,
+};
+typedef struct FecrtpContext {
+    const AVClass *class;
+
+    int kind;
+    int algorithm;
+
+    int ttl;
+    uint8_t pt;
+    const char *host;
+    uint8_t port;
+    int span, every, delay;
+    int protection_length;
+    int col, row;
+
+    int mask_length;    // in bits
+    int long_header;    // if mask_length>16 (L==1) RFC5109 only
+    URLContext *fec_hd;
+    int fec_arr_len;
+    uint64_t mask;
+
+    Fecrtp **fec_arr;
+    uint8_t *rtp_buf;
+    uint16_t rtp_sn;
+    int packet_idx, packet_idx_max;
+    int bitstring_size;
+    int rtp_buf_size;
+    int init;
+    int first;
+    int last_idx;
+} FecrtpContext;
+
+#define OFFSET(x) offsetof(FecrtpContext, x)
+#define E AV_OPT_FLAG_ENCODING_PARAM
+
+static const AVOption options[] = {
+    { "ttl",   "Time to live (in milliseconds, multicast only)", OFFSET(ttl),
+        AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, .flags = E },
+    { "payload_type", "Specify RTP payload type for FEC packets", OFFSET(pt),
+        AV_OPT_TYPE_INT, { .i64 = 98 }, 0, 127, .flags = E },
+    { "port", "Specify RTP port. Default is RTP port + 2", OFFSET(port),
+        AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 127, .flags = E },
+    { "host", "Specify destination host. Default is same as RTP", OFFSET(host),
+        AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, .flags = E },
+    { "kind", "Set the FEC kind",
+      OFFSET(kind), AV_OPT_TYPE_INT, { .i64 = FECRTP_5109 }, 1, 2, E, "kind" },
+        { "parityfec", "parityfec (RFC 2733)",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_2733 }, 1, 2, E, "kind" },
+        { "ulpfec", "ulpfec (RFC 5109)",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_5109 }, 1, 2, E, "kind" },
+    { "algorithm", "Set the covered packets algorithm",
+      OFFSET(algorithm), AV_OPT_TYPE_INT, { .i64 = FECRTP_ALGO_SIMPLE }, 1, 3, E, "algorithm" },
+        { "simple", "Simple: use span/every/delay",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_ALGO_SIMPLE }, 1, 3, E, "algorithm" },
+        { "rotate", "Rotating: combine (span-1) packets in the last (span) packets in every way.",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_ALGO_ROTATE }, 1, 3, E, "algorithm" },
+        { "1d", "1D: column mode (similar to ST2022-1). Use col/row",
+          0, AV_OPT_TYPE_CONST, { .i64 = FECRTP_ALGO_1D }, 1, 3, E, "algorithm" },
+    { "span",  "Number of packets covered each time (algorithm=simple,rotate)", OFFSET(span),
+        AV_OPT_TYPE_INT, { .i64 =  2 }, 2, 24, .flags = E },
+    { "every", "Insert a FEC packet every # RTP packets (algorithm=simple)", OFFSET(every),
+        AV_OPT_TYPE_INT, { .i64 =  2 }, 1, 24, .flags = E },
+    { "delay", "Send FEC packet # packets after last covered (algorithm=simple)", OFFSET(delay),
+        AV_OPT_TYPE_INT, { .i64 =  0 }, 0, 24, .flags = E },
+    { "col", "Number of matrix column (algorithm=1d)", OFFSET(col),
+        AV_OPT_TYPE_INT, { .i64 =  4 }, 2, 24, .flags = E },
+    { "row", "Number of matrix row (algorithm=1d)", OFFSET(row),
+        AV_OPT_TYPE_INT, { .i64 =  4 }, 2, 24, .flags = E },
+
+    { NULL }
+};
+
+static const AVClass fecrtp_class = {
+    .class_name = "fecrtp",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
+static void xor_fast(const uint8_t *in1, int size1, const uint8_t *in2, int size2, uint8_t *out, int size) {
+    int i, n, s, sizemin;
+#if HAVE_FAST_64BIT
+    uint64_t v1, v2;
+#else
+    uint32_t v1, v2;
+#endif
+
+    size = FFMAX(size1, size2);
+    sizemin = FFMIN(size1, size2);
+
+    // Do the XOR where both have data
+#if HAVE_FAST_64BIT
+    n = sizemin / sizeof (uint64_t);
+    s = n * sizeof (uint64_t);
+
+    for (i = 0; i < n; i++) {
+        v1 = AV_RN64A(in1);
+        v2 = AV_RN64A(in2);
+        AV_WN64A(out, v1 ^ v2);
+        in1 += 8;
+        in2 += 8;
+        out += 8;
+    }
+#else
+    n = sizemin / sizeof (uint32_t);
+    s = n * sizeof (uint32_t);
+
+    for (i = 0; i < n; i++) {
+        v1 = AV_RN32A(in1);
+        v2 = AV_RN32A(in2);
+        AV_WN32A(out, v1 ^ v2);
+        in1 += 4;
+        in2 += 4;
+        out += 4;
+    }
+#endif
+
+    n = sizemin - s;
+
+    for (i = 0; i < n; i++) {
+        out[i] = in1[i] ^ in2[i];
+    }
+    s += n;
+
+    // Compute the part where only one has data (padding 0)
+    n = size - s;
+    if (n > 0) {
+        if (size1 >= size2) {
+            memcpy(out,in1, n);
+        } else {
+            memcpy(out,in2, n);
+        }
+    }
+}
+
+static uint16_t bitrev16(uint16_t x)
+{
+       x = (((x & 0xaaaa) >> 1) | ((x & 0x5555) << 1));
+       x = (((x & 0xcccc) >> 2) | ((x & 0x3333) << 2));
+       x = (((x & 0xf0f0) >> 4) | ((x & 0x0f0f) << 4));
+       return((x >> 8) | (x << 8));
+}
+
+static uint32_t bitrev32(uint32_t x)
+{
+       x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1));
+       x = (((x & 0xcccccccc) >> 2) | ((x & 0x33333333) << 2));
+       x = (((x & 0xf0f0f0f0) >> 4) | ((x & 0x0f0f0f0f) << 4));
+       x = (((x & 0xff00ff00) >> 8) | ((x & 0x00ff00ff) << 8));
+    return((x >> 16) | (x << 16));
+}
+
+static int fecrtp_init_fecpacket(URLContext *h, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+    int idx;
+
+    s->last_idx++;
+    if (s->last_idx == s->fec_arr_len)
+        s->last_idx = 0;
+    idx = s->last_idx;
+
+    // sanity check only, should not happen if algorithm are handled properly.
+    if (s->fec_arr[idx]->size>0) {
+        av_log(h, AV_LOG_ERROR, "Internal error, buffer already used (%d)\n", idx);
+        return AVERROR(EINVAL);
+    }
+
+    s->fec_arr[idx]->sn = AV_RB16(buf + 2);
+    // The SSRC value will generally be the same as the SSRC value of the media stream it protects
+    // It MAY be different if the FEC stream is being demultiplexed via the SSRC
+    s->fec_arr[idx]->ssrc = AV_RB32(buf + 8);
+    // Initialize it with the content
+    memcpy(s->fec_arr[idx]->bitstring, buf, size);
+    s->fec_arr[idx]->size = size;
+    s->fec_arr[idx]->length_recovery = (size-12);
+
+    //av_log(h, AV_LOG_DEBUG, "Starting new FEC[%d] SN=%hu SSRC=%X size=%d (packet idx %d)\n",
+        //idx, s->fec_arr[idx]->sn, s->fec_arr[idx]->ssrc, s->fec_arr[idx]->size, s->packet_idx);
+    return 0;
+}
+
+static int fecrtp_add_fecpacket(URLContext *h, int idx, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+
+    if (s->fec_arr[idx]->size>0) {
+        //av_log(h, AV_LOG_DEBUG, "Adding to FEC[%d] (packet idx %d)\n", idx, s->packet_idx);
+
+        xor_fast(s->fec_arr[idx]->bitstring, s->fec_arr[idx]->size,
+            buf, size,
+            s->fec_arr[idx]->bitstring, FFMAX(size, s->fec_arr[idx]->size));
+        s->fec_arr[idx]->length_recovery ^= (size-12);
+        if (s->fec_arr[idx]->size < size) {
+            s->fec_arr[idx]->size = size;
+        }
+    }
+    return 0;
+}
+
+static int fecrtp_write_fec2733(URLContext *h, Fecrtp *fec, uint32_t ts_current, uint64_t mask) {
+    FecrtpContext *s = h->priv_data;
+    uint8_t *buf = s->rtp_buf; // zero-filled
+    uint8_t *b = fec->bitstring;
+    uint16_t sn;
+    int ret;
+
+    sn = ++s->rtp_sn;
+
+    // RTP Header (12 bytes)
+    // V=2, P=xor, X=xor, CC=xor
+    buf[0] = 0x80| (b[0] & 0x3f);
+    // M=xor, PT=fixed
+    buf[1] = (b[1] & 0x80) | s->pt;
+    // SN=ours
+    AV_WB16(buf + 2, sn);
+    // TS=current
+    AV_WB32(buf + 4, ts_current);
+    // SSRC=original
+    AV_WB32(buf + 8, fec->ssrc);
+    // no CSRC or extension, even if bits X or E are set.
+
+    // FEC Header (12 bytes)
+    // SN:original first
+    AV_WB16(buf + 12, fec->sn);
+    // length recovery:xor
+    AV_WB16(buf + 14, fec->length_recovery);
+    // E=0, PT=xor
+    buf[16]=(b[1] & 0X7f);
+    // MASK:MASK (MSb First)
+    AV_WB24(buf + 17, mask);
+    // TS:xor
+    memcpy(buf + 20, b + 4, 4);
+
+    // Payload : part after basic RTP header (12 bytes) of all frames
+    memcpy(buf + 24, b + 12, fec->size-12);
+
+    ret = ffurl_write(s->fec_hd, buf, 24 + fec->size - 12);
+    return ret;
+}
+
+static int fecrtp_write_fec5109(URLContext *h, Fecrtp *fec, uint32_t ts_current, uint64_t mask) {
+    FecrtpContext *s = h->priv_data;
+    uint8_t *buf = s->rtp_buf; // zero-filled
+    uint8_t *b = fec->bitstring;
+    uint16_t sn;
+    int ret;
+    int headerlen;
+
+    sn = ++s->rtp_sn;
+
+    // RTP Header (12 bytes)
+    // V=2, P=0, X=0, CC=0
+    buf[0] = 0x80;
+    // M=0, PT=fixed
+    buf[1] = s->pt;
+    // SN=ours
+    AV_WB16(buf + 2, sn);
+    // TS=current
+    AV_WB32(buf + 4, ts_current);
+    // SSRC=original
+    AV_WB32(buf + 8, fec->ssrc);
+    // no CSRC
+
+    // FEC Header (10 bytes)
+    // E=0, L=0|1, P,X,CC:xor
+    buf[12] = (s->long_header<<6) | (b[0] & 0x3F);
+    // M,PT:xor
+    buf[13] = b[1];
+    // SN:original first
+    AV_WB16(buf + 14, fec->sn);
+    // TS:xor
+    memcpy(buf + 16, b + 4, 4);
+    // length:xor
+    AV_WB16(buf + 20, fec->length_recovery);
+
+    // FEC Level 0 Header
+    // Protection Length: note clear in RFC, guess this is the level payload length
+    AV_WB16(buf + 22, fec->size-12);
+    // Mask : (LSb First)
+    AV_WB16(buf + 24, bitrev16(mask));
+    headerlen = 24+2;
+    if (s->long_header) {
+        mask >>= 16;
+        AV_WB32(buf + 26, bitrev32(mask));
+        headerlen += 4;
+    }
+    // Payload : part after basic RTP header (12 bytes) of all frames
+    memcpy(buf + headerlen, b + 12, fec->size-12);
+
+    ret = ffurl_write(s->fec_hd, buf, headerlen + fec->size - 12);
+    return ret;
+}
+
+static int fecrtp_send_fecpacket(URLContext *h, int idx, const uint8_t *buf, uint64_t mask) {
+    FecrtpContext *s = h->priv_data;
+    uint32_t ts_current;
+    int ret = 0;
+
+    // Sanity check, should not happen if algorithm are handled properly.
+    if (!s->fec_arr[idx]->size) {
+        av_log(h, AV_LOG_ERROR, "Internal error, want to send uninitialized buffer (%d)\n", idx);
+        return AVERROR(EINVAL);
+    }
+
+    // The timestamp MUST be set to the value of the media
+    // RTP clock at the instant the FEC packet is transmitted
+    ts_current = AV_RB32(buf + 4);
+    switch (s->kind) {
+    case FECRTP_2733:
+        if ((ret = fecrtp_write_fec2733(h, s->fec_arr[idx], ts_current, mask)) < 0)
+            goto end;
+        break;
+    case FECRTP_5109:
+        if ((ret = fecrtp_write_fec5109(h, s->fec_arr[idx], ts_current, mask)) < 0)
+            goto end;
+        break;
+    };
+    // mark packet as free for reuse (internal check)
+    s->fec_arr[idx]->size = 0;
+
+end:
+    return ret;
+}
+
+static int fecrtp_open(URLContext *h, const char *uri, int flags) {
+    FecrtpContext *s = h->priv_data;
+    AVDictionary *udp_opts = NULL;
+    int rtp_port, fec_port;
+    char rtp_hostname[256];
+    const char *hostname;
+    char buf[1024];
+
+    s->fec_hd = NULL;
+
+    av_url_split(NULL, 0, NULL, 0, rtp_hostname, sizeof (rtp_hostname), &rtp_port,
+            NULL, 0, uri);
+
+    if (s->port) {
+        fec_port = s->port;
+    } else {
+        if (rtp_port < 1 || rtp_port > UINT16_MAX - 2) {
+            av_log(h, AV_LOG_ERROR, "Invalid RTP base port %d\n", rtp_port);
+            return AVERROR(EINVAL);
+        }
+        fec_port = rtp_port + 2;
+    }
+    if (s->host) {
+        hostname = s->host;
+    } else {
+        hostname = rtp_hostname;
+    }
+
+    if (s->ttl > 0) {
+        av_dict_set_int(&udp_opts, "ttl", s->ttl, 0);
+    }
+
+    ff_url_join(buf, sizeof (buf), "udp", NULL, hostname, fec_port, NULL);
+    if (ffurl_open_whitelist(&s->fec_hd, buf, flags, &h->interrupt_callback,
+            &udp_opts, h->protocol_whitelist, h->protocol_blacklist, h) < 0)
+        goto fail;
+
+    h->max_packet_size = s->fec_hd->max_packet_size;
+    s->init = 1;
+
+    av_dict_free(&udp_opts);
+    return 0;
+
+fail:
+    ffurl_closep(&s->fec_hd);
+    av_dict_free(&udp_opts);
+    return AVERROR(EIO);
+}
+
+static int fecrtp_init(URLContext *h, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+    uint32_t seed;
+    int i;
+    uint64_t mask_bit;
+
+    s->fec_arr = NULL;
+    s->rtp_buf = NULL;
+
+    if (size < 12 || size > UINT16_MAX + 12) {
+        av_log(h, AV_LOG_ERROR, "Invalid RTP packet size\n");
+        return AVERROR_INVALIDDATA;
+    }
+
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        if ( (s->span < s->every) || (s->span % s->every)!=0 ) {
+            av_log(h, AV_LOG_ERROR, "'span' must be a multiple of 'every'\n");
+            return AVERROR_INVALIDDATA;
+        }
+        s->mask_length = s->span;
+        break;
+    case FECRTP_ALGO_ROTATE:
+        s->mask_length = s->span - 1;
+        break;
+    case FECRTP_ALGO_1D:
+        s->span = s->row * s->col;
+        s->mask_length = s->row * s->col;
+        break;
+    };
+
+    switch (s->kind) {
+    case FECRTP_2733:
+        if (s->mask_length > 24) {
+            av_log(h, AV_LOG_ERROR, "Invalid FEC parameters: maximum mask is 24 bits\n");
+            return AVERROR_INVALIDDATA;
+        }
+        break;
+    case FECRTP_5109:
+        s->long_header = (s->mask_length > 16)? 1 : 0;
+        if (s->mask_length > 48) {
+            av_log(h, AV_LOG_ERROR, "Invalid FEC parameters: maximum mask is 48 bits\n");
+            return AVERROR_INVALIDDATA;
+        }
+        break;
+    };
+    s->mask=0;
+    mask_bit=1;
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        for (i=0;i<s->span;i++) {
+            s->mask |= mask_bit;
+            mask_bit <<= 1;
+        }
+        s->fec_arr_len = s->span / s->every + s->delay;
+        // Round up packet index to a multiple of fec_arr_len
+        s->packet_idx_max = INT_MAX - (INT_MAX % s->fec_arr_len);
+        break;
+    case FECRTP_ALGO_ROTATE:
+        // mask will change each time, by removing 1 bit
+        s->mask = (1<<s->span) -1;
+        s->fec_arr_len = s->span;
+        // Round up packet index to a multiple of fec_arr_len
+        s->packet_idx_max = INT_MAX - (INT_MAX % s->fec_arr_len);
+        break;
+    case FECRTP_ALGO_1D:
+        for (i=0;i< s->row;i++) {
+            s->mask |= mask_bit;
+            mask_bit <<= s->col;
+        }
+        s->fec_arr_len = s->col * 2;
+        // Round up packet index to a multiple of fec_arr_len
+        s->packet_idx_max = INT_MAX - (INT_MAX % (s->col * s->row));
+        break;
+    };
+
+    s->packet_idx = 0;
+    if (h->flags & AVFMT_FLAG_BITEXACT) {
+        s->rtp_sn = 0;
+    } else {
+        seed = av_get_random_seed();
+        s->rtp_sn = seed & 0x0fff;
+    }
+
+    if (s->kind == FECRTP_2733) {
+        s->rtp_buf_size = 24 + h->max_packet_size; // 12 + 12: RTP + FEC headers
+        s->bitstring_size = 10 + h->max_packet_size; // 10: P, X, CC, M, PT, SN, TS, Length
+    } else /* if (s->kind == FECRTP_5109) */ {
+        s->rtp_buf_size = 28 + (s->protection_length?s->protection_length:h->max_packet_size); // 12 + 16: RTP + FEC headers
+        s->bitstring_size = 10 + (s->protection_length?s->protection_length:h->max_packet_size); // 10: P, X, CC, M, PT, SN, TS, Length
+    }
+
+    s->fec_arr = av_malloc_array(s->fec_arr_len, sizeof (Fecrtp*));
+    if (!s->fec_arr) {
+        goto fail;
+    }
+    for (i = 0; i < s->fec_arr_len; i++) {
+        s->fec_arr[i] = av_malloc(sizeof (Fecrtp));
+        if (!s->fec_arr[i]) {
+            goto fail;
+        }
+        s->fec_arr[i]->size=0;
+        s->fec_arr[i]->bitstring = av_malloc_array(s->bitstring_size, sizeof (uint8_t));
+        if (!s->fec_arr[i]->bitstring) {
+            av_freep(&s->fec_arr[i]);
+            goto fail;
+        }
+    }
+    // Simplifying: first one will be 0 in array
+    s->last_idx = s->fec_arr_len-1;
+
+    s->rtp_buf = av_malloc_array(s->rtp_buf_size, sizeof (uint8_t));
+    if (!s->rtp_buf) {
+        goto fail;
+    }
+    memset(s->rtp_buf, 0, s->rtp_buf_size);
+
+    s->init = 0;
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        s->first = s->span + s->delay - 1;
+        av_log(h, AV_LOG_INFO, "FEC: %s algorithm simple, span=%d every=%d delay=%d\n",
+            s->kind==FECRTP_5109?"ulpfec":"parityfec", s->span, s->every, s->delay);
+        break;
+    case FECRTP_ALGO_ROTATE:
+        s->first = 0;
+        av_log(h, AV_LOG_INFO, "FEC: %s algorithm rotate, span=%d\n",
+            s->kind==FECRTP_5109?"ulpfec":"parityfec", s->span);
+        break;
+    case FECRTP_ALGO_1D:
+        s->first = s->col * s->row;
+        av_log(h, AV_LOG_INFO, "FEC: %s algorithm 1d, col=%d, row=%d\n",
+            s->kind==FECRTP_5109?"ulpfec":"parityfec", s->col, s->row);
+        break;
+    };
+
+    return 0;
+
+fail:
+    av_log(h, AV_LOG_ERROR, "Failed to allocate the FEC buffer\n");
+    return AVERROR(ENOMEM);
+}
+
+static int fecrtp_write(URLContext *h, const uint8_t *buf, int size) {
+    FecrtpContext *s = h->priv_data;
+    int idx, first_is_new=0;
+    int ret = 0;
+    int protected_size = size;
+    uint64_t mask_clear;
+    int cur_row, cur_col;
+
+    if (s->kind == FECRTP_5109) {
+        // if protection_length is set, forget all after
+        if (s->protection_length > 0 && protected_size > s->protection_length)
+            protected_size = s->protection_length;
+    }
+
+    if (s->init && ((ret = fecrtp_init(h, buf, protected_size)) < 0))
+        goto end;
+
+    if (protected_size > s->bitstring_size) {
+        av_log(h, AV_LOG_ERROR, "The RTP packet size exceed the max_packet_size\n");
+        return AVERROR(EINVAL);
+    }
+
+    idx = s->last_idx;
+    // Create/Update needed FEC packets
+    switch (s->algorithm) {
+    case FECRTP_ALGO_SIMPLE:
+        if (s->packet_idx % s->every == 0) {
+            if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                goto end;
+
+            // Do not xor this one
+            first_is_new = 1;
+        }
+        // One RTP packet will be used in (span/every) FEC packets
+        for (int n=0; n < s->span/s->every; n++) {
+            if (first_is_new) {
+                first_is_new--;
+            } else {
+                // next one to process
+                if (!idx)
+                    idx = s->fec_arr_len;
+                idx--;
+                if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                    goto end;
+            }
+        }
+        break;
+    case FECRTP_ALGO_ROTATE:
+        // comments for case span==4
+        if (s->packet_idx % s->span == 0) {
+            // create all but last (a,b,c) (a,b,d) (a,c,d)
+            for (int n=0; n < s->span-1; n++) {
+                if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                    goto end;
+            }
+            // idx is on last
+        } else if (s->packet_idx % s->span == 1) {
+            // create last now (b,c,d)
+            if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                goto end;
+            // And XOR all but two last (last just created)
+            for (int n=0; n < s->span-2; n++) {
+                // Add the xor to all but
+                idx=s->last_idx+1+n;
+                if (idx >= s->fec_arr_len)
+                    idx -= s->fec_arr_len;
+                if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                    goto end;
+            }
+            // idx is on last-1
+        } else {
+            // XOR all but last-packet_idx
+            for (int n=0; n < s->span; n++) {
+                idx=s->last_idx+1+n;
+                if (idx >= s->fec_arr_len)
+                    idx -= s->fec_arr_len;
+                if (n != (s->span - 1 - (s->packet_idx % s->span))) {
+                    if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                        goto end;
+                }
+            }
+        }
+        break;
+    case FECRTP_ALGO_1D:
+        // Where are we in matrix
+        cur_col = s->packet_idx % s->col;
+        cur_row = (s->packet_idx / s->col ) % s->row;
+        if (!cur_row) {
+            // First row, we create the FEC at each column
+            if ((ret = fecrtp_init_fecpacket(h, buf, protected_size)) <0)
+                goto end;
+        } else {
+            // we process current column
+            idx = (s->last_idx - s->col + 1) + cur_col;
+            if (idx >= s->fec_arr_len)
+                idx -= s->fec_arr_len;
+            if ((ret=fecrtp_add_fecpacket(h, idx, buf, protected_size)) < 0)
+                goto end;
+        }
+        break;
+    };
+
+    // Send needed FEC packets
+    if (s->first) {
+        // Not enough data to send
+        //av_log(h, AV_LOG_DEBUG, "not sending (first=%d)\n", s->first);
+        s->first--;
+    } else {
+        switch (s->algorithm) {
+        case FECRTP_ALGO_SIMPLE:
+            // Should we send now ?
+            if ((s->packet_idx - (s->span-1) - s->delay) % s->every == 0) {
+                // Skip the delay if needed
+                idx-=s->delay+1;
+                if (idx < 0)
+                    idx += s->fec_arr_len;
+                if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask)) < 0)
+                    goto end;
+            }
+            break;
+        case FECRTP_ALGO_ROTATE:
+            // comments for case span==4
+            if (s->packet_idx % s->span == s->span - 2) {
+                // Send first one at one before last
+                mask_clear=1<<(s->span-1);  // This one is not in the xor
+                idx=s->last_idx+1;  // circular -> go first
+                if (idx >= s->fec_arr_len)
+                    idx -= s->fec_arr_len;
+                if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask & (~mask_clear))) < 0)
+                    goto end;
+            } else if (s->packet_idx % s->span == s->span - 1) {
+                // Send all others on last
+                for (int n=1; n < s->span; n++) {
+                    mask_clear=1<<(s->span-1-n);  // This one is not in the xor
+                    // For the last one, we started one later, so clear MSB
+                    if (n == s->span-1)
+                        mask_clear=1<<(s->span-1);
+                    idx=s->last_idx+1+n;
+                    if (idx >= s->fec_arr_len)
+                        idx -= s->fec_arr_len;
+                    if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask & (~mask_clear))) < 0)
+                        goto end;
+                }
+            }
+            break;
+        case FECRTP_ALGO_1D:
+            // cur_col and cur_row already set to where we are in matrix
+            // evenly space them, starting of 1st of matrix
+            // we have s->col to send in s->col*s->row packets
+            if ((cur_col+cur_row*s->col)%s->row == 0) {
+                // Find index of first of previous matrix
+                if (!cur_row) {
+                    // only cur_col has been added for new matrix
+                    idx = (s->last_idx - cur_col + s->col);
+                } else {
+                    // all have been added  for new matrix
+                    idx = (s->last_idx  + 1);
+                }
+                idx += (cur_col+cur_row*s->col)/s->row;
+                idx %= s->fec_arr_len;
+                if ((ret=fecrtp_send_fecpacket(h, idx, buf, s->mask)) < 0)
+                    goto end;
+            }
+            break;
+        };
+    }
+
+    // prepare for next packet
+    s->packet_idx++;
+    if (s->packet_idx == s->packet_idx_max)
+        s->packet_idx = 0;
+
+    ret = protected_size;
+
+end:
+    return ret;
+}
+
+static int fecrtp_close(URLContext *h) {
+    FecrtpContext *s = h->priv_data;
+    int i;
+
+    ffurl_closep(&s->fec_hd);
+
+    if (s->fec_arr) {
+        for (i = 0; i < s->fec_arr_len; i++) {
+            av_free(s->fec_arr[i]->bitstring);
+            av_freep(&s->fec_arr[i]);
+        }
+        av_freep(&s->fec_arr);
+    }
+    av_freep(&s->rtp_buf);
+
+    return 0;
+}
+
+const URLProtocol ff_fecrtp_protocol = {
+    .name                      = "fecrtp",
+    .url_open                  = fecrtp_open,
+    .url_write                 = fecrtp_write,
+    .url_close                 = fecrtp_close,
+    .priv_data_size            = sizeof(FecrtpContext),
+    .flags                     = URL_PROTOCOL_FLAG_NETWORK,
+    .priv_data_class           = &fecrtp_class,
+};
diff --git a/libavformat/protocols.c b/libavformat/protocols.c
index fb6fabdce5..af16313fdb 100644
--- a/libavformat/protocols.c
+++ b/libavformat/protocols.c
@@ -31,6 +31,7 @@  extern const URLProtocol ff_crypto_protocol;
 extern const URLProtocol ff_data_protocol;
 extern const URLProtocol ff_ffrtmpcrypt_protocol;
 extern const URLProtocol ff_ffrtmphttp_protocol;
+extern const URLProtocol ff_fecrtp_protocol;
 extern const URLProtocol ff_file_protocol;
 extern const URLProtocol ff_ftp_protocol;
 extern const URLProtocol ff_gopher_protocol;
diff --git a/libavformat/rtpproto.c b/libavformat/rtpproto.c
index 7dd6042158..a58472d684 100644
--- a/libavformat/rtpproto.c
+++ b/libavformat/rtpproto.c
@@ -295,7 +295,7 @@  static int rtp_open(URLContext *h, const char *uri, int flags)
             av_log(h, AV_LOG_ERROR, "Failed to parse the FEC protocol value\n");
             goto fail;
         }
-        if (strcmp(fec_protocol, "prompeg")) {
+        if (strcmp(fec_protocol, "prompeg") && strcmp(fec_protocol, "fecrtp")) {
             av_log(h, AV_LOG_ERROR, "Unsupported FEC protocol %s\n", fec_protocol);
             goto fail;
         }