downmixing 5.1 mp4a audio does not work (Panther)

[pecus]

Hi all,

I'm trying to view a matroska file containing 8 streams:

• * Xvid Video
  * Mp4a 5.1 Audio Lang 1
  * Mp4a 5.1 Audio Lang 2
  * Mp4a Stereo Audio Comments
  * 4 streams of subs

The video and stereo audio are fine. 5.1 audio does not downsample correctly (I can only hear the soundtrack, i.e. no voices, no effects). Upon changing the audio track I get: "main: cannot add user channel mixer a52tofloat32"
I tried various settings of the audio filter and core audio options to no avail. Help ?

Setup:
TiBook G4 768Mb Ram Os X 10.3.3 (7F44)
Quicktime 6.5.1
VLC 0.7.2

Debug output:
coreaudio debug: system has [1] device(s)
coreaudio debug: device [0] has name [Built-in Audio]
coreaudio debug: device [0] has [1] streams
coreaudio debug: supported format: [44100][lpcm][30][4][1][4][2][16]
coreaudio debug: getting device [0]
coreaudio debug: stream format: [44100][lpcm][30][4][1][4][2][16]


Thanks

[hans-jürgen]

The video and stereo audio are fine. 5.1 audio does not downsample correctly (I can only hear the soundtrack, i.e. no voices, no effects).

So you mean "downmix", not "downsample", because it seems you cannot hear the Centre and Surround channels.

Upon changing the audio track I get: "main: cannot add user channel mixer a52tofloat32"
Setup:
TiBook G4 768Mb Ram Os X 10.3.3 (7F44)
Quicktime 6.5.1
VLC 0.7.2

Your OS and hardware does not support multichannel playback, as far as I know. So it's necessary that the player downmixes the 5.1 tracks to stereo. It seems that VLC has a problem to enable the correct module, because "a52tofloat32" wouldn't make sense with a 5.1 AAC track (that would afford e.g. the downmixer in FAAD2, the AAC decoder). How did you produce the 5.1 AAC tracks, by the way, with Nero HE AAC or FAAC?

[Guest]

yes, I meant downmix

I havo no idea how the AAC tracks were produced. And there are no "signatures" in the tracks meta info...

[hans-jürgen]

yes, I meant downmix

I havo no idea how the AAC tracks were produced. And there are no "signatures" in the tracks meta info...

It's not that important, only if you would really have problems with the sample rate (HE AAC files have a 22 khz and a 44.1 kHz part). By the way, did you look for a check box that might enable the internal FAAD2 downmixer anywhere? Normally all plugins based on this decoder have it as an option in the GUI...

[pecus]

I've seen there are many issues related to FAAD2 (viewtopic.php?t=1609, some outside this forum as in http://www.audiocoding.com/phorum/read. ... 927&t=4927).
To further help in problemsolving, here's the log regarding choosing the audio mixer:

main debug: selecting ES 0x2
main debug: looking for decoder module
main debug: probing 22 candidates
main debug: using decoder module "faad"
...
faad warning: decoded zero sample
main debug: looking for audio output module
main debug: probing 3 candidates
coreaudio debug: system has [1] device(s)
coreaudio debug: device [0] has name [Built-in Audio]
coreaudio debug: device [0] has [1] streams
coreaudio debug: supported format: [44100][lpcm][30][4][1][4][2][16]
coreaudio debug: getting device [0]
coreaudio debug: stream format: [44100][lpcm][30][4][1][4][2][16]
coreaudio debug: setting format: [44100][lpcm][30][4][1][4][2][16]
...
main debug: using audio output module "coreaudio"
main debug: output 'fl32' 44100 Hz Stereo frame=1 samples/8 bytes
main debug: mixer 'fl32' 44100 Hz Stereo frame=1 samples/8 bytes
main debug: no need for any filter
main debug: looking for audio mixer module
main debug: probing 3 candidates
main debug: using audio mixer module "trivial_mixer"
main debug: input 'fl32' 48000 Hz 3F2R/LFE frame=1 samples/24 bytes
main debug: filter(s) 'fl32'->'fl32' 48000 Hz->48000 Hz 3F2R/LFE->Stereo
main debug: looking for audio filter module
main debug: probing 23 candidates
main debug: using audio filter module "trivial_channel_mixer"
main debug: found a filter for the whole conversion
main debug: filter(s) 'fl32'->'fl32' 52800 Hz->44100 Hz Stereo->Stereo
main debug: looking for audio filter module
main debug: probing 23 candidates

AFAIK it recognizes the stream as a 5.1 (3F2R/LFE) and filters it to Stereo. Sadly acustically it is not so :-\

[The DJ]

Actually, it is, it's just not downmixing. VLC currently doesn't do this properly, it just takes the two front channels instead of downmixing.

A proper downmixing feature will probably be implemented in the next release, though it kinda depends on how much time ppl will have.