[FFmpeg-devel] [PATCH v3 1/4] avformat/movenc: fix assert failure in get_cluster_duration()

[Paul B Mahol]

On Sun, Feb 27, 2022 at 7:49 AM Gyan Doshi <ffmpeg at gyani.pro> wrote:

>
>
> On 2022-02-27 12:04 pm, "zhilizhao(赵志立)" wrote:
> > Ping.
> >
> >> On Dec 31, 2021, at 7:36 PM, Zhao Zhili <quinkblack at foxmail.com> wrote:
> >>
> >> When editlist is disabled, the workaournd method of shift dts to
> >> zero and increase the first sample duration doesn't work if the
> >> timestamp is larger than mp4 spec restriction (e.g., sample_delta
> >> in stts entry). Further more, it triggers get_cluster_duration()
> >> assert failure. This patch will drop large offsets between
> >> multiple tracks.
> >> ---
> >> libavformat/movenc.c | 13 ++++++++++++-
> >> 1 file changed, 12 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> >> index 0f912dd012..f5bb785b01 100644
> >> --- a/libavformat/movenc.c
> >> +++ b/libavformat/movenc.c
> >> @@ -5917,7 +5917,18 @@ int ff_mov_write_packet(AVFormatContext *s,
> AVPacket *pkt)
> >>           * to signal the difference in starting time without an edit
> list.
> >>           * Thus move the timestamp for this first sample to 0,
> increasing
> >>           * its duration instead. */
> >> -        trk->cluster[trk->entry].dts = trk->start_dts = 0;
> >> +        if (pkt->dts + pkt->duration <= INT32_MAX) {
> >> +            trk->cluster[trk->entry].dts = trk->start_dts = 0;
> >> +        } else {
> >> +            /* Impossible to write a sample duration >= UINT32_MAX.
>
> As per 14496-12 (2005), sample_delta is stored as
>
> unsigned int(32) sample_delta;
>
> The only restriction is that no delta shall be zero except the last
> sample, which means UINT32_MAX  is allowed.
> INT32_MAX had been set as max allowed delta in mov.c since inception.
> See my recent changes in mov.c correcting that.
>
> Will this patch break remuxing of files with large deltas?
> Let's not clamp if the spec does not call for it.
>

Yes, I agree 100% this is not proper fix for assert.


> Regards,
> Gyan
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