[FFmpeg-devel] [PATCH v1] lavf/mov: Fix timestamp rescale on sidx atom

[Jun Li]

On Sun, May 12, 2019 at 7:44 PM Jun Li <junli1026 at gmail.com> wrote:

>
>
> On Fri, May 10, 2019 at 7:25 PM Jun Li <junli1026 at gmail.com> wrote:
>
>>
>> On Thu, May 9, 2019 at 2:08 AM Jun Li <junli1026 at gmail.com> wrote:
>>
>>> Fix #5090
>>> Fix the timestamp rescale issue, from sidx timebase to
>>> stream's timebase.
>>> ---
>>>  libavformat/mov.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>>> index 78f692872b..d058855e6c 100644
>>> --- a/libavformat/mov.c
>>> +++ b/libavformat/mov.c
>>> @@ -5017,7 +5017,7 @@ static int mov_read_sidx(MOVContext *c,
>>> AVIOContext *pb, MOVAtom atom)
>>>              return AVERROR_PATCHWELCOME;
>>>          }
>>>          avio_rb32(pb); // sap_flags
>>> -        timestamp = av_rescale_q(pts, st->time_base, timescale);
>>> +        timestamp = av_rescale_q(pts, timescale, st->time_base);
>>>
>>>          index = update_frag_index(c, offset);
>>>          frag_stream_info = get_frag_stream_info(&c->frag_index, index,
>>> track_id);
>>> --
>>> 2.17.1
>>>
>>
>> Ping
>>
>
> This change is for fix the issue of calculating sidx_pts.
> Sidx box has "earliest_presentation_time", used as pts of  the referent
> track, sidx also has timescale field.
> So the operation should convert from sidx's timescale to track's
> timescale, this patch is for addressing this, as well as fixing #5090.
>
> Of course this is based on my understanding, so please correct me if I am
> wrong. Thanks !
>
>
Ping.
I believe this is a bug and triggered whenever sidx box's timescale is
different from track's timescale.
Created this kind of content and verified that ffplay couldn't play while
VLC plays well.
Then I checked VLC's implementation:
https://github.com/videolan/vlc/blob/5609c1b41d6fbca6323103619c6139caf7bc9e6e/modules/demux/mp4/mp4.c#L4735

Hope someone could help to have a review ? Thanks ! :)

Best Regards,
-Jun


> Best Regards,
> Jun
>
>
>
>