Re: [FFmpeg-devel] [PATCH] avformat/movenc: fix VVC encoding with leading pictures

[Gabriel Hege <g+ffmpeg@hege.cc>]

On 17.05.25 04:26, Nuo Mi wrote:
> On Fri, May 16, 2025 at 7:05 PM Gabriel Hege <g+ffmpeg@hege.cc> wrote:
> 
>> This is a resubmission with a corrected commit message.
>>
>>
>> The default behavior for VVenC (since v1.10.0) is to create an IDR with
>> leading pictures for the first picture in decoding order (POC 32). This
>> leads to FFmpeg generating an edit list with an empty entry, skipping
>> the leading pictures.
>>
>> This patch fixes the calculation for the start_pts, while the DTS is
>> negative (as produced by libvvenc).
>>
>>
>> How to reproduce the issue (needs --enable-libvvenc and a recent
>> libvvenc, e.g. v1.13):
>>
> Hi Gabriel,
> Thank you for your patch. It addresses the MP4 issue, but it looks like MKV
> has the same problem as well.

Hi Nuo Mi,

I'm sorry I don't really have an understanding of the MKV format. I had 
a quick look at the code, but the processing seems quite different and I 
didn't really find the corresponding code locations to fix the problem 
there.


> Hi @James Almer <jamrial@gmail.com> ,
> Could you please take a look at the patch when you have a moment? You've
> been the most active contributor to this file recently.
> 
>>
>> Encode VVC directly into MP4 container:
>> ./ffmpeg -i /data/YUV/foreman_352x288_30Hz_i420_8.y4m -an -preset faster
>> -vcodec vvc test.mp4
>>
>>     -> encodes 300 frames.
>>
>> Decode to YUV (or play back using ffplay):
>> ./ffmpeg -i test.mp4 test.yuv
>>
>>     -> outputs 271 frames
>>
>> When dumping the mp4-structure using 'MP4Box -diso test.mp4', I see the
>> following EditListBox, which skips the first couple of
>> frames:<EditListBox Size="40" Type="elst" Version="0" Flags="0"
>> Specification="p12" Container="edts" EntryCount="2">
>> <EditListEntry Duration="1033" MediaTime="-1" MediaRate="1"/>
>> <EditListEntry Duration="8967" MediaTime="18432" MediaRate="1"/>
>> </EditListBox>
>>
>>
>> With the fix applied 300 frames are decoded as expected and the
>> EditListBox looks like this:
>> <EditListBox Size="28" Type="elst" Version="0" Flags="0"
>> Specification="p12" Container="edts" EntryCount="1">
>> <EditListEntry Duration="10000" MediaTime="2560" MediaRate="1"/>
>> </EditListBox>
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