[FFmpeg-devel] [PATCH] avformat/matroskaenc: flag discardable packets as such

[James Almer]

Signed-off-by: James Almer <jamrial at gmail.com>
---
 libavformat/matroskaenc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

This only has an effect when muxing h265 streams originating from the
libx265 wrapper atm, as no other encoder or demuxer currently sets
the flag.

I compared the output of our muxer with the latest mkvmerge, and in
the latter a few more SimpleBlocks were flagged as discardable than
by our muxer after this patch.
I can't say if our libx265 wrapper is not properly flagging what it
should, or if mkvmerge's parser is flagging more frames than it
should.

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index f22c2ab70c..915ef3c107 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -2100,7 +2100,8 @@ static void mkv_write_block(AVFormatContext *s, AVIOContext *pb,
     MatroskaMuxContext *mkv = s->priv_data;
     AVCodecParameters *par = s->streams[pkt->stream_index]->codecpar;
     uint8_t *data = NULL, *side_data = NULL;
-    int offset = 0, size = pkt->size, side_data_size = 0;
+    const int discardable = !!(pkt->flags & AV_PKT_FLAG_DISPOSABLE);
+    int offset = 0, size = pkt->size, side_data_size = 0, flags = 0;
     int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
     uint64_t additional_id = 0;
     int64_t discard_padding = 0;
@@ -2160,12 +2161,15 @@ static void mkv_write_block(AVFormatContext *s, AVIOContext *pb,
         blockid = MATROSKA_ID_BLOCK;
     }
 
+    if (blockid == MATROSKA_ID_SIMPLEBLOCK)
+        flags = (keyframe << 7) | discardable;
+
     put_ebml_id(pb, blockid);
     put_ebml_num(pb, size + 4, 0);
     // this assumes stream_index is less than 126
     avio_w8(pb, 0x80 | track_number);
     avio_wb16(pb, ts - mkv->cluster_pts);
-    avio_w8(pb, (blockid == MATROSKA_ID_SIMPLEBLOCK && keyframe) ? (1 << 7) : 0);
+    avio_w8(pb, flags);
     avio_write(pb, data + offset, size);
     if (data != pkt->data)
         av_free(data);
-- 
2.15.0