[FFmpeg-trac] #10496(undetermined:new): Wrong first audio segment duration when generating dash segments and playlist.mpd

[FFmpeg]

#10496: Wrong first audio segment duration when generating dash segments and
playlist.mpd
-------------------------------------+-------------------------------------
             Reporter:  Mirko Gibin  |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:  DASH         |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 I have a 60fps video with a 48000hz audio track and I want to generate
 dash segments and a playlist MPD from it. Segments need to be of the same
 length (with exclusion of the last one)
 Looking inside the generated playlist.mpd I can see that the first audio
 segments is shorter than the others. If I reproduce the playlist starting
 from segment 1 everything works fine. If I reproduce the playlist starting
 from another segment (e.g. segment 5) audio and video are not in sync.

 How to reproduce:
 The command to generate dash segments is the following one.
 {{{
 ffmpeg -i input.mp4 -c:v libx264 -c:a aac  -dash_segment_type mp4 -f dash
 -g 96 -movflags frag_keyframe+empty_moov+default_base_moof+faststart
 -sc_threshold 0 -seg_duration 1.6 -use_template 1 -use_timeline 1
 playlist.mpd
 }}}

 The generated audio adaptation set is composed as follows:

 {{{
         <AdaptationSet id="1" contentType="audio" startWithSAP="1"
 segmentAlignment="true" bitstreamSwitching="true" lang="und">
                         <Representation id="1" mimeType="audio/mp4"
 codecs="mp4a.40.2" bandwidth="341000" audioSamplingRate="48000">
                                 <AudioChannelConfiguration
 schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011"
 value="6" />
                                 <SegmentTemplate timescale="48000"
 initialization="init-stream$RepresentationID$.m4s" media="chunk-
 stream$RepresentationID$-$Number%05d$.m4s" startNumber="5">
                                         <SegmentTimeline>
                                                 <S t="0" d="75776" />
                                                 <S d="76800" r="35" />
                                                 <S d="39936" />
                                         </SegmentTimeline>
                                 </SegmentTemplate>
                         </Representation>
                 </AdaptationSet>
 }}}

 If you set the startNumber=1 in the playlist on both video and audio
 adaptation sets everything works fine. If you set the startNumber=5 in the
 playlist on both video and audio adaptation sets you can hear and see that
 audio and video are not synchronized.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10496>
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