[FFmpeg-devel] [PATCH] avformat/oggparsevorbis: Fix oggvorbis duration parsing for small files

[Guangyu Sun]

On Thu, May 5, 2022 at 4:05 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.
>
> If the file has multiple pages for the data packets. The duration of the
> last packet can be correctly adjusted without being affected by the first
> packet. But if the first packet and the last packet are located in the
> same page, the duration of the last packet will have an unwanted offset.
>
> This commit fixes https://trac.ffmpeg.org/ticket/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 | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/oggparsevorbis.c b/libavformat/oggparsevorbis.c
> index 289900f7cf..9a486c9fe8 100644
> --- a/libavformat/oggparsevorbis.c
> +++ b/libavformat/oggparsevorbis.c
> @@ -412,6 +412,7 @@ static int vorbis_packet(AVFormatContext *s, int idx)
>      struct ogg_stream *os = ogg->streams + idx;
>      struct oggvorbis_private *priv = os->private;
>      int duration, flags = 0;
> +    int first_page;
>
>      if (!priv->vp)
>          return AVERROR_INVALIDDATA;
> @@ -420,7 +421,8 @@ static int vorbis_packet(AVFormatContext *s, int idx)
>       * here we parse the duration of each packet in the first page and
> compare
>       * the total duration to the page granule to find the encoder delay
> and
>       * set the first timestamp */
> -    if ((!os->lastpts || os->lastpts == AV_NOPTS_VALUE) && !(os->flags &
> OGG_FLAG_EOS) && (int64_t)os->granule>=0) {
> +    first_page = !os->lastpts || os->lastpts == AV_NOPTS_VALUE;
> +    if (first_page && !(os->flags & OGG_FLAG_EOS) &&
> (int64_t)os->granule>=0) {
>          int seg, d;
>          uint8_t *last_pkt  = os->buf + os->pstart;
>          uint8_t *next_pkt  = last_pkt;
> @@ -479,6 +481,13 @@ 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 (first_page && os->segp == 1)
> +            os->pduration = 0;
>      }
>
>      /* final packet handling
> --
> 2.30.1
>
>
Ping.