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From: =?iso-8859-1?Q?J=F6rg_Beckmann?= <Joerg.Beckmann@scisys.com>
To: "ffmpeg-devel@ffmpeg.org" <ffmpeg-devel@ffmpeg.org>
Thread-Topic: [PATCH v5] avformat/mov: Memory optimization with QuickTime/MP4
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Date: Mon, 9 Dec 2019 15:05:01 +0000
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Subject: [FFmpeg-devel] [PATCH v5] avformat/mov: Memory optimization with
	QuickTime/MP4
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Invents a new option "discard_fragments" for the MP4/Quicktime/MOV decoder.
 
If the option is not set, nothing changes at all. If it is set, old fragments
are discarded as far as possible on each call to switch_root. For pure audio
streams, the memory usage is now constant. For video streams, the memory
usage is reduced. It's tested with audio streams received from a 
professional DAB+ receiver and with video streams created on my own with 
"ffmpeg -i <video>.m4v -c:a:0 copy -c:v copy -c:s copy -f ismv -movflags \
frag_keyframe -movflags faststart tcp://localhost:1234?listen" and 
"ffmpeg -i tcp://localhost:1234 -c:a copy -c:v copy -c:s copy -y <output>".

Signed-off-by: Jörg Beckmann <joerg.beckmann@scisys.com>
---
libavformat/isom.h |  1 +
 libavformat/mov.c  | 49 ++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/libavformat/isom.h b/libavformat/isom.h
index 4943b80ccf..9b4753f4d7 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -268,6 +268,7 @@ typedef struct MOVContext {
     int advanced_editlist;
     int ignore_chapters;
     int seek_individually;
+    int discard_fragments;
     int64_t next_root_atom; ///< offset of the next root atom
     int export_all;
     int export_xmp;
diff --git a/libavformat/mov.c b/libavformat/mov.c
index 7553a7fdfc..deb3ff5508 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -7698,8 +7698,11 @@ static int should_retry(AVIOContext *pb, int error_code) {
 
 static int mov_switch_root(AVFormatContext *s, int64_t target, int index)
 {
-    int ret;
+    int ret, i;
     MOVContext *mov = s->priv_data;
+    AVStream *st = NULL;
+    MOVStreamContext *sc;
+    MOVFragment *frag;
 
     if (index >= 0 && index < mov->frag_index.nb_items)
         target = mov->frag_index.item[index].moof_offset;
@@ -7721,6 +7724,43 @@ static int mov_switch_root(AVFormatContext *s, int64_t target, int index)
 
     mov->found_mdat = 0;
 
+    if (mov->discard_fragments) {
+        frag = &mov->fragment;
+
+        for (i = 0; i < mov->fc->nb_streams; i++) {
+            if (mov->fc->streams[i]->id == frag->track_id) {
+                st = mov->fc->streams[i];
+                break;
+            }
+        }
+
+        av_assert0(st);
+
+        sc = st->priv_data;
+
+        switch (st->codecpar->codec_type) {
+            case AVMEDIA_TYPE_AUDIO:
+            case AVMEDIA_TYPE_SUBTITLE:
+                /* Freeing VIDEO tables leads to corrupted video when writing to eg. MKV */
+                av_freep(&st->index_entries);
+                st->nb_index_entries = 0;
+                st->index_entries_allocated_size = 0;
+
+                sc->current_index = 0;
+                sc->current_sample = 0;
+
+                av_freep(&sc->ctts_data);
+                sc->ctts_allocated_size = 0;
+                sc->ctts_count = 0;
+                break;
+        }
+
+        av_free(mov->frag_index.item->stream_info);
+        av_freep(&mov->frag_index.item);
+        mov->frag_index.allocated_size = 0;
+        mov->frag_index.nb_items = 0;
+    }
+
     ret = mov_read_default(mov, s->pb, (MOVAtom){ AV_RL32("root"), INT64_MAX });
     if (ret < 0)
         return ret;
@@ -7975,6 +8015,9 @@ static int mov_read_seek(AVFormatContext *s, int stream_index, int64_t sample_ti
     int sample;
     int i;
 
+    if (mc->discard_fragments)  // Seeking is not possible if fragments are discarded.
+        return AVERROR(ENOTSUP);
+
     if (stream_index >= s->nb_streams)
         return AVERROR_INVALIDDATA;
 
@@ -8063,6 +8106,10 @@ static const AVOption mov_options[] = {
     { "decryption_key", "The media decryption key (hex)", OFFSET(decryption_key), AV_OPT_TYPE_BINARY, .flags = AV_OPT_FLAG_DECODING_PARAM },
     { "enable_drefs", "Enable external track support.", OFFSET(enable_drefs), AV_OPT_TYPE_BOOL,
         {.i64 = 0}, 0, 1, FLAGS },
+    {"discard_fragments",
+            "Discard fragments after they have been read to support live streams.",
+            OFFSET(discard_fragments), AV_OPT_TYPE_BOOL, { .i64 = 0 },
+            0, 1, FLAGS },
 
     { NULL },
 };