[FFmpeg-devel] [PATCH] avformat/oggparsevorbis: Ignore duration of the first packet

[Guangyu Sun]

On Wed, Apr 20, 2022 at 8:22 PM Guangyu Sun <sunguangyucn at gmail.com> wrote:

> The decoded Data is not returned from the first frame; it must be used
> to 'prime' the decode engine. The duration of the first packet should
> be ignored also by the container, to make sure the total duration is
> trimmed correctly.
>
> This commit fixes #6367.
>
> dd if=/dev/zero of=./silence.raw count=1 bs=500
> oggenc --raw silence.raw --output=silence.ogg
> oggdec --raw --output silence.oggdec.raw silence.ogg
> ffmpeg -codec:a libvorbis -i silence.ogg -f s16le -codec:a pcm_s16le
> silence.libvorbis.ffmpeg.raw
> ffmpeg -i silence.ogg -f s16le -codec:a pcm_s16le silence.native.ffmpeg.raw
> ls -l *.raw
>
> Signed-off-by: Guangyu Sun <gsun at roblox.com>
> ---
>  libavformat/oggparsevorbis.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/libavformat/oggparsevorbis.c b/libavformat/oggparsevorbis.c
> index 289900f7cf..1f922b3c7e 100644
> --- a/libavformat/oggparsevorbis.c
> +++ b/libavformat/oggparsevorbis.c
> @@ -479,6 +479,13 @@ static int vorbis_packet(AVFormatContext *s, int idx)
>              flags = 0;
>          }
>          os->pduration = duration;
> +        /* Data is not returned from the first frame; it must be used to
> 'prime'
> +         * the decode engine. The duration of the first packet should be
> ignored
> +         * also by the container, to make sure the total duration is
> trimmed
> +         * correctly.
> +         */
> +        if ((!os->lastpts || os->lastpts == AV_NOPTS_VALUE) && os->segp
> == 1)
> +            os->pduration = 0;
>      }
>
>      /* final packet handling
> --
> 2.30.1
>
>
Ping. This patch fixes audio duration mis-match after transcoding a small
ogg/vorbis file.

Thanks,
Guangyu