Re: [FFmpeg-devel] [PATCH] avformat/vpcc: fix vpcC generation for RTMP

[James Almer <jamrial@gmail.com>]

On 9/2/2023 2:02 PM, Alessandro Ros wrote:
> In order to send VP9 tracks with RTMP, the enhanced RTMP specification
> tells that VPCodecConfigurationRecord, a.k.a. vpcC ISO-BMFF box, must
> be inserted into a metadata message. However, the function responsible
> for generating vpcCs currently returns invalid boxes, that are lacking
> the Version and Flag fields, inherited from FullBox. For some reason,
> both flags were being added manually in movenc. This patch fixes the
> issue.
> 
> Signed-off-by: Alessandro Ros <aler9.dev@gmail.com>
> ---
>   libavformat/movenc.c | 3 ---
>   libavformat/vpcc.c   | 2 ++
>   2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index 7ef6cef46a..696ae5a6c9 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -1441,10 +1441,7 @@ static int mov_write_vpcc_tag(AVFormatContext *s, 
> AVIOContext *pb, MOVTrack *tra
>        avio_wb32(pb, 0);
>       ffio_wfourcc(pb, "vpcC");
> -    avio_w8(pb, 1); /* version */
> -    avio_wb24(pb, 0); /* flags */
>       ff_isom_write_vpcc(s, pb, track->vos_data, track->vos_len, 
> track->par);
> -
>       return update_size(pb, pos);
>   }
> 
> diff --git a/libavformat/vpcc.c b/libavformat/vpcc.c
> index ea66959abf..256407dd6d 100644
> --- a/libavformat/vpcc.c
> +++ b/libavformat/vpcc.c
> @@ -208,6 +208,8 @@ int ff_isom_write_vpcc(AVFormatContext *s, 
> AVIOContext *pb,
>       if (ret < 0)
>           return ret;
> 
> +    avio_w8(pb, 1); /* version */
> +    avio_wb24(pb, 0); /* flags */
>       avio_w8(pb, vpcc.profile);
>       avio_w8(pb, vpcc.level);
>       avio_w8(pb, (vpcc.bitdepth << 4) | (vpcc.chroma_subsampling << 1) 
> | vpcc.full_range_flag);

This will change the output of the flv muxer. It might be for the 
better, since now both these values will be added to it, but it would be 
best to know that first.
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