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

[John Stebbins]

On 12/13/2017 07:14 PM, James Almer wrote:
> 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);

LGTM. 

FYI, I have a pending patch that does the same thing (in a slightly different way) as well as a patch for reading the discardable flag from mkv files.  But I wanted to wait till my other patches related to the discardable flag were fully reviewed and
accepted before adding more to the list.  As a reminder, there is still a patch to set discardable flag in the x264 encoder, a patch to read the flag in mp4 and a patch to use the flag in ffplay that are not yet accepted, though there are no unresolved
comments for these patch submissions.

-- 
John      GnuPG fingerprint: D0EC B3DB C372 D1F1 0B01  83F0 49F1 D7B2 60D4 D0F7


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 488 bytes
Desc: OpenPGP digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20171215/07e16d5a/attachment.sig>