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

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2022-07-05 07:05 pm, "zhilizhao(赵志立)" wrote:
>
>> 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.

It's not about hoping that it works.  It's about not preventing the user 
from acquiring the stream payload.

Can you test if setting -discard:d none -i INPUT allows reading the 
stream with your patch?

Regards,
Gyan

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