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

[Guangyu Sun <sunguangyucn@gmail.com>]

On Mon, May 9, 2022 at 11:19 AM Guangyu Sun <sunguangyucn@gmail.com> wrote:

> On Thu, May 5, 2022 at 4:05 PM Guangyu Sun <sunguangyucn@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@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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