[mythtv-commits] Ticket #8366: aac background music in foreground / little to no actor's dialogue audible

[MythTV]

#8366: aac background music in foreground / little to no actor's dialogue audible
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 Reporter:  Johnny Walker <johnnyjboss@…>          |       Owner:  jyavenard 
     Type:  defect                                 |      Status:  new       
 Priority:  minor                                  |   Milestone:  0.24      
Component:  MythTV - Audio Output                  |     Version:  Trunk Head
 Severity:  low                                    |     Mlocked:  0         
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Changes (by jyavenard):

  * milestone:  0.23 => 0.24


Comment:

 We never did support downmix, we always relied on ffmpeg to do the job ...

 When we ask ffmpeg to decode audio content, we provides as an argument the
 number of channels to be decoded.
 The number of channels is what has been set up in the general settings
 (value is either 2 or 6)

 That part of the code hasn't change in ages (it's in libavdecoder...

 If you are decoding a 5.1 audio file yet asked ffmpeg to only decode for 2
 channels ; ffmpeg will downmix for some codec (AC3); but most will not be
 downmixed. This includes AAC

 Note that the behaviour is different depending on what library was used to
 decode AAC.
 If decoded with libfaad, then the downmix will happen, because libfaad
 does support it.

 IF compiled using ffmpeg internal AAC decoder, then no downmix will occur.

 The problem is in ffmpeg, not mythtv.

 I'm willing to bet that this file didn't play properly in 0.22 either if
 compiled with the same options as the 0.23 was compiled :)

 As a workaround, compile mythtv with the option --enable-libfaad

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Ticket URL: <http://svn.mythtv.org/trac/ticket/8366#comment:5>
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