[FFmpeg-devel,1/4] avformat/aviobuf: fix flushing write buffers after seeking backward or forward

Submitted by Marton Balint on June 18, 2017, 10:02 p.m.

Details

Message ID 20170618220254.21682-1-cus@passwd.hu
State Accepted
Commit c14fa7a330f634738003bee731f17ff4c5717228
Headers show

Commit Message

Marton Balint June 18, 2017, 10:02 p.m.
This patch makes aviobuf work more like traditinal file IO, which is how people
think about it.

For example, in the past, aviobuf only flushed buffers until the current buffer
position, even if more data was written to it previously, and a backward seek
was used to reposition the IO context.

From now, aviobuf will keep track of the written data, so no explicit seek will
be required till the end of the buffer, or till the end of file before flushing.

This fixes at least one regression, fate-vsynth3-flv was broken if
flush_packets option was set to false, an explicit seek was removed in
4e3cc4bdd8acedbcc703607ed0efbb64bb5c3cc4.

Also from now on, if a forward seek in the write buffer were to cause a gap
between the already written data and the new file position, a flush will
happen.

The must_flush varable is also removed, which might have caused needless
flushes with multiple seeks whithin the write buffer. Since we know the amount
of data written to it, we will know when to flush.

Signed-off-by: Marton Balint <cus@passwd.hu>
---
 libavformat/avio.h    | 42 ++++++++++++++++++++++++++----------------
 libavformat/aviobuf.c | 26 ++++++++++++++------------
 libavformat/version.h |  2 +-
 3 files changed, 41 insertions(+), 29 deletions(-)

Comments

Michael Niedermayer June 19, 2017, 3:01 p.m.
On Mon, Jun 19, 2017 at 12:02:51AM +0200, Marton Balint wrote:
> This patch makes aviobuf work more like traditinal file IO, which is how people
> think about it.
> 
> For example, in the past, aviobuf only flushed buffers until the current buffer
> position, even if more data was written to it previously, and a backward seek
> was used to reposition the IO context.
> 
> From now, aviobuf will keep track of the written data, so no explicit seek will
> be required till the end of the buffer, or till the end of file before flushing.
> 
> This fixes at least one regression, fate-vsynth3-flv was broken if
> flush_packets option was set to false, an explicit seek was removed in
> 4e3cc4bdd8acedbcc703607ed0efbb64bb5c3cc4.
> 
> Also from now on, if a forward seek in the write buffer were to cause a gap
> between the already written data and the new file position, a flush will
> happen.
> 
> The must_flush varable is also removed, which might have caused needless
> flushes with multiple seeks whithin the write buffer. Since we know the amount
> of data written to it, we will know when to flush.
> 
> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
>  libavformat/avio.h    | 42 ++++++++++++++++++++++++++----------------
>  libavformat/aviobuf.c | 26 ++++++++++++++------------
>  libavformat/version.h |  2 +-
>  3 files changed, 41 insertions(+), 29 deletions(-)

Iam in favor of this patch

thx

[...]

Patch hide | download patch | download mbox

diff --git a/libavformat/avio.h b/libavformat/avio.h
index 525eb7129e..844a5723d3 100644
--- a/libavformat/avio.h
+++ b/libavformat/avio.h
@@ -168,8 +168,9 @@  typedef struct AVIOContext {
     const AVClass *av_class;
 
     /*
-     * The following shows the relationship between buffer, buf_ptr, buf_end, buf_size,
-     * and pos, when reading and when writing (since AVIOContext is used for both):
+     * The following shows the relationship between buffer, buf_ptr,
+     * buf_ptr_max, buf_end, buf_size, and pos, when reading and when writing
+     * (since AVIOContext is used for both):
      *
      **********************************************************************************
      *                                   READING
@@ -196,21 +197,24 @@  typedef struct AVIOContext {
      *                                   WRITING
      **********************************************************************************
      *
-     *                                          |          buffer_size          |
-     *                                          |-------------------------------|
-     *                                          |                               |
+     *                             |          buffer_size                 |
+     *                             |--------------------------------------|
+     *                             |                                      |
      *
-     *                                       buffer              buf_ptr     buf_end
-     *                                          +-------------------+-----------+
-     *                                          |/ / / / / / / / / /|           |
-     *  write buffer:                           | / to be flushed / |           |
-     *                                          |/ / / / / / / / / /|           |
-     *                                          +-------------------+-----------+
+     *                                                buf_ptr_max
+     *                          buffer                 (buf_ptr)       buf_end
+     *                             +-----------------------+--------------+
+     *                             |/ / / / / / / / / / / /|              |
+     *  write buffer:              | / / to be flushed / / |              |
+     *                             |/ / / / / / / / / / / /|              |
+     *                             +-----------------------+--------------+
+     *                               buf_ptr can be in this
+     *                               due to a backward seek
      *
-     *                                         pos
-     *               +--------------------------+-----------------------------------+
-     *  output file: |                          |                                   |
-     *               +--------------------------+-----------------------------------+
+     *                            pos
+     *               +-------------+----------------------------------------------+
+     *  output file: |             |                                              |
+     *               +-------------+----------------------------------------------+
      *
      */
     unsigned char *buffer;  /**< Start of the buffer. */
@@ -226,7 +230,7 @@  typedef struct AVIOContext {
     int (*write_packet)(void *opaque, uint8_t *buf, int buf_size);
     int64_t (*seek)(void *opaque, int64_t offset, int whence);
     int64_t pos;            /**< position in the file of the current buffer */
-    int must_flush;         /**< true if the next seek should flush */
+    int must_flush;         /**< unused */
     int eof_reached;        /**< true if eof reached */
     int write_flag;         /**< true if open for writing */
     int max_packet_size;
@@ -329,6 +333,12 @@  typedef struct AVIOContext {
     int (*short_seek_get)(void *opaque);
 
     int64_t written;
+
+    /**
+     * Maximum reached position before a backward seek in the write buffer,
+     * used keeping track of already written data for a later flush.
+     */
+    unsigned char *buf_ptr_max;
 } AVIOContext;
 
 /**
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 1667e9f08b..dcb91570d8 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -91,6 +91,7 @@  int ffio_init_context(AVIOContext *s,
     s->orig_buffer_size =
     s->buffer_size = buffer_size;
     s->buf_ptr     = buffer;
+    s->buf_ptr_max = buffer;
     s->opaque      = opaque;
     s->direct      = 0;
 
@@ -100,7 +101,6 @@  int ffio_init_context(AVIOContext *s,
     s->read_packet     = read_packet;
     s->seek            = seek;
     s->pos             = 0;
-    s->must_flush      = 0;
     s->eof_reached     = 0;
     s->error           = 0;
     s->seekable        = seek ? AVIO_SEEKABLE_NORMAL : 0;
@@ -171,15 +171,16 @@  static void writeout(AVIOContext *s, const uint8_t *data, int len)
 
 static void flush_buffer(AVIOContext *s)
 {
-    if (s->write_flag && s->buf_ptr > s->buffer) {
-        writeout(s, s->buffer, s->buf_ptr - s->buffer);
+    s->buf_ptr_max = FFMAX(s->buf_ptr, s->buf_ptr_max);
+    if (s->write_flag && s->buf_ptr_max > s->buffer) {
+        writeout(s, s->buffer, s->buf_ptr_max - s->buffer);
         if (s->update_checksum) {
             s->checksum     = s->update_checksum(s->checksum, s->checksum_ptr,
-                                                 s->buf_ptr - s->checksum_ptr);
+                                                 s->buf_ptr_max - s->checksum_ptr);
             s->checksum_ptr = s->buffer;
         }
     }
-    s->buf_ptr = s->buffer;
+    s->buf_ptr = s->buf_ptr_max = s->buffer;
     if (!s->write_flag)
         s->buf_end = s->buffer;
 }
@@ -228,8 +229,10 @@  void avio_write(AVIOContext *s, const unsigned char *buf, int size)
 
 void avio_flush(AVIOContext *s)
 {
+    int seekback = s->write_flag ? FFMIN(0, s->buf_ptr - s->buf_ptr_max) : 0;
     flush_buffer(s);
-    s->must_flush = 0;
+    if (seekback)
+        avio_seek(s, seekback, SEEK_CUR);
 }
 
 int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
@@ -269,8 +272,9 @@  int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
         short_seek = s->short_seek_threshold;
 
     offset1 = offset - pos; // "offset1" is the relative offset from the beginning of s->buffer
-    if (!s->must_flush && (!s->direct || !s->seek) &&
-        offset1 >= 0 && offset1 <= buffer_size - s->write_flag) {
+    s->buf_ptr_max = FFMAX(s->buf_ptr_max, s->buf_ptr);
+    if ((!s->direct || !s->seek) &&
+        offset1 >= 0 && offset1 <= (s->write_flag ? s->buf_ptr_max - s->buffer : buffer_size)) {
         /* can do the seek inside the buffer */
         s->buf_ptr = s->buffer + offset1;
     } else if ((!(s->seekable & AVIO_SEEKABLE_NORMAL) ||
@@ -299,7 +303,6 @@  int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
         int64_t res;
         if (s->write_flag) {
             flush_buffer(s);
-            s->must_flush = 1;
         }
         if (!s->seek)
             return AVERROR(EPIPE);
@@ -308,7 +311,7 @@  int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
         s->seek_count ++;
         if (!s->write_flag)
             s->buf_end = s->buffer;
-        s->buf_ptr = s->buffer;
+        s->buf_ptr = s->buf_ptr_max = s->buffer;
         s->pos = offset;
     }
     s->eof_reached = 0;
@@ -994,7 +997,7 @@  int ffio_set_buf_size(AVIOContext *s, int buf_size)
     s->buffer = buffer;
     s->orig_buffer_size =
     s->buffer_size = buf_size;
-    s->buf_ptr = buffer;
+    s->buf_ptr = s->buf_ptr_max = buffer;
     url_resetbuf(s, s->write_flag ? AVIO_FLAG_WRITE : AVIO_FLAG_READ);
     return 0;
 }
@@ -1052,7 +1055,6 @@  int ffio_rewind_with_probe_data(AVIOContext *s, unsigned char **bufp, int buf_si
     s->pos = buf_size;
     s->buf_end = s->buf_ptr + buf_size;
     s->eof_reached = 0;
-    s->must_flush = 0;
 
     return 0;
 }
diff --git a/libavformat/version.h b/libavformat/version.h
index b00a8b0333..1fb8ffb2b9 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -32,7 +32,7 @@ 
 // Major bumping may affect Ticket5467, 5421, 5451(compatibility with Chromium)
 // Also please add any ticket numbers that you believe might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  57
-#define LIBAVFORMAT_VERSION_MINOR  73
+#define LIBAVFORMAT_VERSION_MINOR  74
 #define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \