[FFmpeg-trac] #6983(avcodec:new): AAC encoder breaking 5.1 channels

FFmpeg trac at avcodec.org
Thu Jan 25 17:53:55 EET 2018

#6983: AAC encoder breaking 5.1 channels
             Reporter:  elsiko   |                     Type:  defect
               Status:  new      |                 Priority:  normal
            Component:  avcodec  |                  Version:  git-master
             Keywords:           |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  0        |
 Summary of the bug:
 For a long time now, I've been doing some encodings into x265/aac using
 Recently I started noticing a problem with the audio channels that get - I
 think - mixed up.

 The original file media info would show:
 `Front: L C R, Side: L R, LFE`

 But the encoded file will show:
 `Front: L C R, Side: C, Back: L R`

 I'm no expert, but I think the LFE channel is either dropped or converted.
 I think this behaviour started around December 2017.

 To be certain that something indeed changed, I encoded a file twice, used
 two static builds (from here: https://johnvansickle.com/ffmpeg/), once
 using a build from 2017-09-02, and one from 2018-01-24.

 I attached to the tickets the logs of both encodings, the media info (+
 the original).
 You can download the original mkv file, as well as encoded files from

 You can clearly see in the mediainfo of 2017 that the channels were
 correct (with LFE), but that's not the case in the 2018 encoding.

 One last thing, I think this problem might be related to this ticket:

Ticket URL: <https://trac.ffmpeg.org/ticket/6983>
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