Yeah, OK, so I really could have been a lot clearer about this. Let’s try this again. :)
Basically there are really two ways to do surround-sound: hardware-decoded and software-decoded. In the former, much more common and simpler case, you just get your media application, like iTunes or DVD player, to send AC3/DTS over the SPDIF, and the rest is down to your decoder. From a historic perspective, this is not so different from the days of analog Dolby ProLogic, which used phase-shifting to encode surround tracks over a stereo line; the hack works because the natively-stereo SPDIF interface can be fed, and then recognise, a digital AC3/DTS stream. This method is used by your Apple TV, and yes, iTunes movies do indeed include an AC3 track for this purpose. DTS uses a similar (slightly less compressed, but still ultimately lossy) approach. The SPDIF is usable, otherwise, for lossless stereo output. Both encoded and unencoded data cannot be sent over the SPDIF simultaneously, of course. In the latter, your Mac does all the decoding. The audio device is merely 5.1 (or whatever) output, each channel separately addressable. iTunes and DVD Player will not use software decoding for AC3 5.1 (but DVD Player will downmix as necessary to stereo). Other formats take up the slack, like WAV or AAC, but you need alternative software, like VLC, if you are to get software-decoding of AC3 without the pass-through. Naturally, using this method gives you the most choice (unless DRM gets involved), but is also the hardest to get right and the least convenient if you are intending on walking the golden path set by most studio-endorsed software and hardware combinations. In an ideal world there’d be a way to perform on-the-fly encoding of non-dolby-digital data to an audio receiver over the one port, but it doesn’t work like that. And there’s no software to allow your computer to receive digital data for decoding to an analog audio output device, probably because it’d violate some licensing agreement or other, but there are decoder devices out there that you know where you can get them from that’ll take up the slack here. Now, I hope I have explained things adequately. :) -- The following information is important for all members of the Mac Visionaries list. If you have any questions or concerns about the running of this list, or if you feel that a member's post is inappropriate, please contact the owners or moderators directly rather than posting on the list itself. Your Mac Visionaries list moderator is Mark Taylor and your owner is Cara Quinn - you can reach Cara at caraqu...@caraquinn.com The archives for this list can be searched at: http://www.mail-archive.com/macvisionaries@googlegroups.com/ --- You received this message because you are subscribed to the Google Groups "MacVisionaries" group. To unsubscribe from this group and stop receiving emails from it, send an email to macvisionaries+unsubscr...@googlegroups.com. To post to this group, send email to macvisionaries@googlegroups.com. Visit this group at https://groups.google.com/group/macvisionaries. For more options, visit https://groups.google.com/d/optout.
