[FFmpeg-user] copyts flag behavior on ffmpeg5 and ffmpeg6 in dash format

[Mirko Gibin]

Hi everybody,

I want to change resolution to only a subset of dash fragments and keep
their original timestamp.
With ffmpeg v4.3.1 I used the following command:
cat init.mp4 seg-N.m4s | ffmpeg -i pipe:0 -filter_complex
'[0]split=1[s0];[s0]scale=1280:720[s1]' -map '[s1]' -c:v libx264
 -dash_segment_type mp4 -f dash -g 60 -media_seg_name seg-N.m4s -movflags
frag_keyframe+empty_moov+default_base_moof+faststart playlist.mpd -copyts
(with N=1, 2, 3 ....)
The output fragments maintained the original timestamp, I can see that in
the SIDX box the earliest_presentation_time is different for each fragment
and equals to the original.

With ffmpeg5 and ffmpeg6 the previous command does not keep the original
timestamp, and I can see that in the SIDX box the
eraliest_presentation_time is 0 for each fragment.

Has something changed with the usage of the copyts flag? I cannot
understand if this is a bug introduced in newer ffmpeg versions or the
wanted behavior, since the sequence_number in MFHD box is always resetted
to 0 in each version of Ffmpeg I mentioned.

Best,
Mirko
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