[FFmpeg-trac] #6915(avformat:new): DASH audio segments duration doesn't match exactly with video segments duration.

FFmpeg trac at avcodec.org
Tue Dec 19 05:46:03 EET 2017

#6915: DASH audio segments duration doesn't match exactly with video segments
             Reporter:  beloko      |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avformat
              Version:  git-master  |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |

Comment (by beloko):

 I know the specification about the #EXT-X-TARGETDURATION since its first

 In this audio stream playlist some .m4s segments have a duration of
 4.010667 seconds. So to be compliant with the specification
 #EXT-X-TARGETDURATION is rounded to the upper value 5. It's correct.

 The issue is about playback and synchronisation for smooth streaming. With
 multiple video bitrate streams and audio tracks at adaptive bitrate, the
 video player switch automatically to different quality according to the
 bandwidth. When a video or an audio track isn't cut exactly at the same
 duration, sometimes spectator can detect a video freeze, a strange click
 noise in the audio rendering. Or the voice is a bit desynchronized with
 the mouth that's speaking.

 The Apple mediastreamvalidator tool check the #EXT-X-TARGETDURATION is the
 same for all embed streams/tracks specified as a #EXT-X-STREAM-INF:. And
 returns this kind of error message if the longest segment duration is
 different between streams/tracks.

 Error: Different target durations detected
 --> Detail:  Target duration: 4 vs Target duration: 5
 --> Source:  hdready/tears_of_steel_4k_2112_720p.m3u8
 --> Compare: veryhigh/tears_of_steel_4k_1056_480p.m3u8

 So to be square with the required specification all segment duration
 should be 4 seconds long exactly.

Ticket URL: <https://trac.ffmpeg.org/ticket/6915#comment:2>
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