#5122: First audio packet is always corrupted when parsing PCM
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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 |
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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
apparent.
Attached screenshots of our analyzer tool show some examples of the issues
mentioned.
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
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Ticket URL: <https://trac.ffmpeg.org/ticket/5122>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker
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