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

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2022-02-27 12:04 pm, "zhilizhao(赵志立)" wrote:
> Ping.
>
>> On Dec 31, 2021, at 7:36 PM, Zhao Zhili <quinkblack@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.

Regards,
Gyan
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