> On Mar 1, 2022, at 9:32 PM, zhilizhao(赵志立) <quinkbl...@foxmail.com> wrote:
>
>
>> On Feb 27, 2022, at 2:49 PM, Gyan Doshi <ffm...@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 <quinkbl...@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.
>
> Since get_cluster_duration() checks dts against INT_MAX, remove
> the clamp at here can still trigger abort() after.
>
> ```
> av_assert0(next_dts <= INT_MAX);
>
> ```
>
> The prototype of get_cluster_duration() which returns int needs
> to be fixed, and a bunch of places.
>
> And then we can get regression issues: movenc.c output files with
> delta larger than INT32_MAX can be dangerous, which is not the
> case of mov.c demuxer.
>
> It’s a clever trick here, by using a large sample duration to
> handle start time difference between multiple tracks. Since it’s
> not a standard method like editlist, I think we can turn off the
> strategy safely (FFmpeg abort before the patch, so it’s already
> turned off in a hard way).
>
> What do you think?
Ping. Another idea is return error instead of abort().
>
>>
>> Regards,
>> Gyan
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