Re: [FFmpeg-devel] [PATCH 2/2 v2] avformat/demux: extract extradata from packets when context update is requested

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

James Almer:
> If the demuxer doesn't set extradata in the stream's codecpar, a
> need_context_update request will delete the previously extracted extradata in
> the stream's internal AVCodecContext.
> As we can't ensure the old extradata is valid for the stream in its post
> context update request state, try to get extradata from the new packet instead
> of attempting to preserve the old in some form.
> 
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>  libavformat/demux.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/demux.c b/libavformat/demux.c
> index abfd5fee7d..39aa1cd4e3 100644
> --- a/libavformat/demux.c
> +++ b/libavformat/demux.c
> @@ -1319,6 +1319,8 @@ fail:
>      return ret;
>  }
>  
> +static int extract_extradata(FFFormatContext *si, AVStream *st, const AVPacket *pkt);
> +
>  static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
>  {
>      FFFormatContext *const si = ffformatcontext(s);
> @@ -1373,6 +1375,11 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
>                  return ret;
>              }
>  
> +            if (!sti->avctx->extradata &&
> +                (ret = extract_extradata(si, st, pkt)) < 0) {
> +                av_packet_unref(pkt);
> +                return ret;
> +            }
>              sti->codec_desc = avcodec_descriptor_get(sti->avctx->codec_id);
>  
>              sti->need_context_update = 0;
> @@ -2470,6 +2477,8 @@ static int extract_extradata(FFFormatContext *si, AVStream *st, const AVPacket *
>      if (ret < 0)
>          return ret;
>  
> +    av_bsf_flush(sti->extract_extradata.bsf);
> +
>      ret = av_bsf_send_packet(sti->extract_extradata.bsf, pkt_ref);
>      if (ret < 0) {
>          av_packet_unref(pkt_ref);
> @@ -3090,7 +3099,8 @@ find_stream_info_err:
>          err = codec_close(sti);
>          if (err < 0 && ret >= 0)
>              ret = err;
> -        av_bsf_free(&sti->extract_extradata.bsf);
> +        if (sti->extract_extradata.bsf)
> +            av_bsf_flush(sti->extract_extradata.bsf);
>      }
>      if (ic->pb) {
>          FFIOContext *const ctx = ffiocontext(ic->pb);

This will keep the BSF around for longer than necessary, although only a
tiny minority of demuxers ever set need_context_update at all.

- Andreas

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