AC3 Virtual sound device

[daniel@…]

This is a total side thing, but my friends and I have been *thinking* about writing a virtual sound driver for OSX to get around this spdif out problem.

Goal:

• Create a virtual sound device that presents itsself as 6 channels.
• Encode audio on the fly using a52
• Push the freshly encoded audio out the physical sound device spdif

Do you think modern macs are fast enough to decode video and audio, display video and re-encode audio in near real time?? As component developers do you think this is even feasable?

[gbooker]

This could be feasible. It would solve other problems like the fact there is no way to play 5.1 AAC audio through the spdif interface. The problem is all the a52 libraries I have seen are decode only; they don't encode. I have messed with AC3 encoders in the past, and I think that modern macs should be fast enough to do this real-time.

Truthfully, Apple should be the ones to do passthrough. They know about it; they just choose to do nothing about it. Your time may be better spent demanding that Apple do this. Everything I read indicates there is no licensing issues with AC3 passthrough, so they have no excuse whatsoever. The only built-in App that I know of that can use AC3 passthrough is the DVD player (and front row using it). IMHO, that is not enough to be worth buying a dolby decoder to connect to a mac.

[Mark]

Hi, I've only just found this codec after Googling for a Quicktime plugin to decode AC3 5.1 sound tracks. For what it's worth, VLC is capable of pushing out 5.1 channel surround sound over s/pdif. This is what I currently use on my Core Duo Mac Mini but I'd far rather use QuickTime and Front Row. Would there be anything in the VLC source code which might help here?

 http://www.videolan.org/vlc

Mark (at clamxav dot com)

[rojailal@…]

A virtual AC3 sound device would be useful to people like me who have a USB spdif output (Maudio in this case) to play 5.1 AAC audio files. Not even VLC can play these in full surround sound for me, and I don't even think it'll work with the spdif Apple includes. You HAVE to have a 5.1 sound card, which is kind of lame.

Also, i don't know how intensive it would be, but can a 1.5Ghz G4 encode that kind of 5.1 audio on the fly for it to be worth it?

[anonymous]

I've also noticed that VLC can output encoded AC3 (passthrough) over s/pdif, but I would rather use Quicktime as the player of choice. So please add my vote to add this same functionality to your AC3 component.

Thanks

[gbooker]

Replying to anonymous:

I've also noticed that VLC can output encoded AC3 (passthrough) over s/pdif, but I would rather use Quicktime as the player of choice. So please add my vote to add this same functionality to your AC3 component. Thanks

As I said in #4, this is up to apple to do. This is not the job of a Quicktime component, rather the application.

[anonymous]

Replying to daniel@chote.net:

A on-the-fly ac3-encoder would be a solution to many problems I think. There is a somewhat outdated attempt to do this in the environment of the JACK-project. It is called ac3jack and can be found at  http://essej.net/ac3jack/. Maybe somebody more gifted than I am can use this as a basis for something new.

[Kris]

While surfing for a dolby digital playing solution in quicktime I found this site:  http://www.43folders.com/2007/03/30/apple-tv-5-1-audio/#comment-13532 It seems that on my mac mini with the volume turned to 100% in iTunes my receiver will detect the dolby digital stream send out from the mac in PCM 44.1kHz. So are there any possibilities that a52 decoder could send the stream as PCM 44.1kHz. Then all people with an receiver capable of decoding dolby digital should get 5.1 sound in quicktime applications

[gbooker]

Kris, look at #4 and you will see I already did this. This ticket is for other things, such as viewing HD content in 5.1 AAC and re-encoding that as AC3 so that a receiver can decode it.