Re: [FFmpeg-devel] [PATCH] avformat/mov: discard data streams with all zero sample_delta

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Jul 5, 2022, at 8:07 PM, Gyan Doshi <ffmpeg@gyani.pro> wrote:
> 
> 
> 
> On 2022-07-05 01:20 pm, Zhao Zhili wrote:
>> From: Zhao Zhili <zhilizhao@tencent.com>
>> 
>> Streams with all zero sample_delta in 'stts' have all zero dts.
>> They have higher chance be chose by mov_find_next_sample(), which
>> leads to seek again and again.
>> 
>> For example, GoPro created a 'GoPro SOS' stream:
>>   Stream #0:4[0x5](eng): Data: none (fdsc / 0x63736466), 13 kb/s (default)
>>     Metadata:
>>       creation_time   : 2022-06-21T08:49:19.000000Z
>>       handler_name    : GoPro SOS
>> 
>> With 'ffprobe -show_frames http://example.com/gopro.mp4', ffprobe
>> blocks until all samples in 'GoPro SOS' stream are consumed first.
>> 
>> Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
>> ---
>>  libavformat/mov.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>> 
>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>> index 88669faa70..2a4eb79f27 100644
>> --- a/libavformat/mov.c
>> +++ b/libavformat/mov.c
>> @@ -3062,6 +3062,20 @@ static int mov_read_stts(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>>      st->nb_frames= total_sample_count;
>>      if (duration)
>>          st->duration= FFMIN(st->duration, duration);
>> +
>> +    // All samples have zero duration. They have higher chance be chose by
>> +    // mov_find_next_sample, which leads to seek again and again.
>> +    //
>> +    // It's AVERROR_INVALIDDATA actually, but such files exist in the wild.
>> +    // So only mark data stream as discarded for safety.
>> +    if (!duration && sc->stts_count &&
>> +            st->codecpar->codec_type == AVMEDIA_TYPE_DATA) {
>> +        av_log(c->fc, AV_LOG_WARNING,
>> +               "All samples in data stream index:id [%d:%d] have zero duration, "
>> +               "discard the stream\n",
>> +               st->index, st->id);
>> +        st->discard = AVDISCARD_ALL;
>> +    }
>>      sc->track_end = duration;
>>      return 0;
>>  }
> 
> So this will allow audio and video streams to be demuxed, but not data?  That distinction seems arbitrary.

Disable audio/video streams may create regression. It’s unlikely for random
and broken data stream.

> 
> Print a warning and assign a duration to each sample. Either 1 or if not zero/Inf, st->duration/st->nb_frames.

Set sample_duration to 1 doesn’t work. Dts still far behind other streams.

Set sample_duration st->duration/st->nb_frames works for me, but I prefer
current strategy for the following reasons:

1. AVDISCARD_ALL is more close to AVERROR_INVALIDDATA by giving up instead
of trying correction and hope it works, which may not, e.g., st->duration
is broken, or bad interleave even though we fixed sample_duration.

2. libavformat users can enable the stream and get the original dts/duration,
if they want to.

> 
> Regards,
> Gyan
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