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

[Guangyu Sun]

On Mon, May 16, 2022 at 5:05 PM Guangyu Sun <sunguangyucn at gmail.com> wrote:
>
> On Mon, May 9, 2022 at 11:19 AM Guangyu Sun <sunguangyucn at gmail.com> wrote:
>
> > 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.
> >
> Ping again. This patch fixes an oggvorbis transcode issue.
> https://devforum.roblox.com/t/recent-changes-to-uploaded-audio-compressionprocessing-causing-timing-drift/1735440/10
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Ping. Any feedback about this patch?