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

FFmpeg trac at avcodec.org
Tue Jan 5 14:50:14 CET 2016

#5122: First audio packet is always corrupted when parsing PCM
             Reporter:               |                    Owner:
  marcel_poelstra                    |                   Status:  new
                 Type:  defect       |                Component:
             Priority:  normal       |  undetermined
              Version:  git-master   |               Resolution:
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |

Comment (by marcel_poelstra):

 I know about the preroll data.  In the libfdk this is most apparent since
 it just adds an empty packet. In that case the problem I'm talking about
 is in the second packet. This is clearly visible in the screenshots I
 Furthermore, when I encode the same source wav with different tools, the
 "garbage" packet (so not the mentioned 'preroll' but really the packet
 with random data) is not there in all cases.
 It just happens with ffmpeg. So one might conclude that something (like a
 pcm parser component) is effecting the source PCM to cause this.

 The reason I'm putting this up is, that we run in to files on our VOD
 platform that simply refuse to play. Common factor is, they all contain
 this garbage in the first or, in case of libfdk, the second packet.  So
 the actual payload might be perfect, but still the decoder refuses to
 play. Files that do not have these garbage packets always play fine.

 Replying to [comment:10 heleppkes]:
 > Note that AAC encoders often produce "preroll" data thats supposed to
 not be played, but just decoded to "prime" the decoder.

Ticket URL: <https://trac.ffmpeg.org/ticket/5122#comment:11>
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