[FFmpeg-trac] #5122(undetermined:new): First audio packet is always corrupted when parsing PCM

FFmpeg trac at avcodec.org
Tue Jan 5 13:25:25 CET 2016

#5122: First audio packet is always corrupted when parsing PCM
             Reporter:               |                     Type:  defect
  marcel_poelstra                    |                 Priority:  important
               Status:  new          |                  Version:  git-
            Component:               |  master
  undetermined                       |               Blocked By:
             Keywords:  audio        |  Reproduced by developer:  0
  artifacts pcm aac                  |
             Blocking:               |
Analyzed by developer:  0            |
 Summary of the bug:

 The following issue came up while investigating a suspected issue with hls
 streams, where always the first AAC audio packet in the first segment
 seemed to be filled with garbage.
 During investigation we also discovered that the exact symptoms varied
 with the different codec options (like libfdk or native ffmpeg aac).
 While searching for the best codec (with the less amount of artifacts), it
 appeared that the generated garbage was actually created while parsing the
 source PCM audio. It looks like the aac artifacts in the first packet we
 saw initially, were just caused by this.
 In short: copying a pcm source file through ffmpeg causes damage to the
 first audio packet of 1024 samples in the outputfile.
 Once this output is being encoded into e.g. aac, the effect is even more

 Attached screenshots of our analyzer tool show some examples of the issues

 How to reproduce:
 % ffmpeg -i  testin.wav  -c:a copy  testout.wav
 ffmpeg version git-master
 built on Jan.5th 2016

 Best regards
 Marcel Poelstra
 SBS Broadcasting, The Netherlands

Ticket URL: <https://trac.ffmpeg.org/ticket/5122>
FFmpeg <https://ffmpeg.org>
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