[FFmpeg-trac] #5179(undetermined:new): Native AAC encoder does not respect channelmap assignments

FFmpeg trac at avcodec.org
Fri Jan 22 14:48:49 CET 2016


#5179: Native AAC encoder does not respect channelmap assignments
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             Reporter:  mulvya       |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by atomnuker):

 The AAC specifications define only the most common channel map per a given
 number of channels.

 From the code:
 >    // 1 channel  - single channel element
 >    // 2 channels - channel pair
 >    // 3 channels - center + stereo
 >    // 4 channels - front center + stereo + back center
 >    // 5 channels - front center + stereo + back stereo
 >    // 6 channels - front center + stereo + back stereo + LFE
 >    // 7 channels - invalid without PCE
 >    // 8 channels - front center + front stereo + side stereo + back
 stereo + LFE

 So without support for Programmable Channel Elements (PCE) which
 theoretically allow for custom mapping the encoder cannot output anything
 outside of those defined presets. Our encoder doesn't support those, and I
 doubt any other encoder does. I also doubt many decoders support these and
 correctly do the mapping. So you're out of luck if you still want to use
 AAC.

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Ticket URL: <https://trac.ffmpeg.org/ticket/5179#comment:1>
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