5.1 output through Griffin Firewave

Hmm... works for 6 channel aac output but not 5.1 output from an ac3 file? That is weird. Does it give you 5.1 audio output when you play a DVD?

The way the codec is designed, it doesn't actually talk to the hardware. Instead, it will be given compressed audio samples, and asked to decompress them into discrete audio channels.

I am not one to pass up free hardware, but I am not sure if I can make it work. I have already given up on the s/pdif interface and I have the connector on both of my computers.

It works for 5.1 from a DVD, and VLC seems to be able to use it *as usual*. The only weird thing with VLC is that it seems to be very channel specific (ie. The center channel only sits on the center channel, however when playing the DVD version of the same movie with DVD player, the center channel seems to sit across L,R,C a little more evenly.)

In Audio Midi Setup, it shows as available 5.1/Quadraphonic items in the multichannel dropdown... and has the ability to specify the channel number.... Im guessing thats how quicktime maps up the channels for 6 channel aac.

In quicktime, you can also change any track to a different channel output and it passes it correctly to which ever you specify.

I dont know if your implementation passes out all the channels or not, I havent looked at the code yet. But in my preliminary tests I still only got 2 channels out.

Replying to gbooker:

Hmm... works for 6 channel aac output but not 5.1 output from an ac3 file? That is weird. Does it give you 5.1 audio output when you play a DVD? The way the codec is designed, it doesn't actually talk to the hardware. Instead, it will be given compressed audio samples, and asked to decompress them into discrete audio channels. I am not one to pass up free hardware, but I am not sure if I can make it work. I have already given up on the s/pdif interface and I have the connector on both of my computers.

The problem seems to be that Quicktime only see's the movie as having 2 channels. Im sure this would work if Quicktime got to see the movie as having 6 (in the right order too).

-Dan

Replying to daniel@chote.net:

It works for 5.1 from a DVD, and VLC seems to be able to use it *as usual*. The only weird thing with VLC is that it seems to be very channel specific (ie. The center channel only sits on the center channel, however when playing the DVD version of the same movie with DVD player, the center channel seems to sit across L,R,C a little more evenly.) In Audio Midi Setup, it shows as available 5.1/Quadraphonic items in the multichannel dropdown... and has the ability to specify the channel number.... Im guessing thats how quicktime maps up the channels for 6 channel aac. In quicktime, you can also change any track to a different channel output and it passes it correctly to which ever you specify. I dont know if your implementation passes out all the channels or not, I havent looked at the code yet. But in my preliminary tests I still only got 2 channels out. Replying to gbooker:

Hmm... works for 6 channel aac output but not 5.1 output from an ac3 file? That is weird. Does it give you 5.1 audio output when you play a DVD? The way the codec is designed, it doesn't actually talk to the hardware. Instead, it will be given compressed audio samples, and asked to decompress them into discrete audio channels. I am not one to pass up free hardware, but I am not sure if I can make it work. I have already given up on the s/pdif interface and I have the connector on both of my computers.

Replying to daniel@chote.net:

The problem seems to be that Quicktime only see's the movie as having 2 channels. Im sure this would work if Quicktime got to see the movie as having 6 (in the right order too). -Dan

Are these .avi files? If so, the problem could be that some avi importers like to claim that the audio is only two channel, and as such, quicktime takes the importer's word.

Yeah, they are .avi's... Encoded with XVid.

Replying to anonymous:

Replying to daniel@chote.net:

The problem seems to be that Quicktime only see's the movie as having 2 channels. Im sure this would work if Quicktime got to see the movie as having 6 (in the right order too). -Dan

Are these .avi files? If so, the problem could be that some avi importers like to claim that the audio is only two channel, and as such, quicktime takes the importer's word.

I just tried a .ac3 sample, and it plays back multichannel perfectly. Do you know of any avi impoters that work?

Replying to anonymous:

Replying to daniel@chote.net:

The problem seems to be that Quicktime only see's the movie as having 2 channels. Im sure this would work if Quicktime got to see the movie as having 6 (in the right order too). -Dan

Are these .avi files? If so, the problem could be that some avi importers like to claim that the audio is only two channel, and as such, quicktime takes the importer's word.

I know I did this somehow, but now for the life of me, I can't remember. Off-hand, I don't know of any, but the Perian Project likely will eventually.

Replying to anonymous:

I just tried a .ac3 sample, and it plays back multichannel perfectly. Do you know of any avi impoters that work?

Im actually hacking around in aviimporter-r7. It seems that it has a self enforced hack to limit to 2 channels:

if(asbd.mChannelsPerFrame > 2)

asbd.mChannelsPerFrame = 2;

I commented that out and recompiled and I actually got 6 discrete channels, all mono of course. Im about to crack open the ac3movieimport code to see how the audiochannellayout stuff gets used.

Thanks for your help -Dan

Replying to gbooker:

I know I did this somehow, but now for the life of me, I can't remember. Off-hand, I don't know of any, but the Perian Project likely will eventually. Replying to anonymous:

I just tried a .ac3 sample, and it plays back multichannel perfectly. Do you know of any avi impoters that work?

Perian has the same issue. I can fix it there in a much more useful way (it would have the ability to set the audiochannellayout correctly).

BTW, the channel order is: left, right, center, lfe screen, left surround, right surround.

Replying to daniel@chote.net:

Im actually hacking around in aviimporter-r7. It seems that it has a self enforced hack to limit to 2 channels: if(asbd.mChannelsPerFrame > 2) asbd.mChannelsPerFrame = 2; I commented that out and recompiled and I actually got 6 discrete channels, all mono of course. Im about to crack open the ac3movieimport code to see how the audiochannellayout stuff gets used. Thanks for your help -Dan

With a quick hack to aviimporter things work great. I dont know how far away a release of Perian is, so I dont know if its worth me cleaning up the hack and making it a little more flexable.

The one thing I need to do is figure out why the center channel is so distinct from the rest when used like this. Playing a DVD sounds quite a bit different than it does with A52 (both codec through quicktime, and vlc).

Replying to gbooker:

Perian has the same issue. I can fix it there in a much more useful way (it would have the ability to set the audiochannellayout correctly). BTW, the channel order is: left, right, center, lfe screen, left surround, right surround. Replying to daniel@chote.net:

Im actually hacking around in aviimporter-r7. It seems that it has a self enforced hack to limit to 2 channels: if(asbd.mChannelsPerFrame > 2) asbd.mChannelsPerFrame = 2; I commented that out and recompiled and I actually got 6 discrete channels, all mono of course. Im about to crack open the ac3movieimport code to see how the audiochannellayout stuff gets used. Thanks for your help -Dan

Perian is preparing for a 0.5 release (first version). It has 6 active developers, half have done components before, and the other half are from the adium team. It has many great aspirations, and will continue to see active development. Some part will need to be re-architected to make things work better, but this is certainly on the list of items we want for it.

I currently use it as my only solution for playing back divx and flv (youtube and google video) files. It is faster in CPU than the divx.com codecs.

Replying to daniel@chote.net:

With a quick hack to aviimporter things work great. I dont know how far away a release of Perian is, so I dont know if its worth me cleaning up the hack and making it a little more flexable. The one thing I need to do is figure out why the center channel is so distinct from the rest when used like this. Playing a DVD sounds quite a bit different than it does with A52 (both codec through quicktime, and vlc).

Closing this because changeset 256 in perian's repository fixes this problem. It ignores the settings in the AVI file and parses the data in the AC3 stream to determine the sample rate and number of channels.