This thread is still confusing... attempt to clear it up
Maybe it's good to start with the basics again:
To get multichannel sound into
content files, you have basically 2 options:
- Encode the channels into a proprietary compressed data stream (AC3, DTS, AAC, WMA) and let the player hardware or software deal with it
- Provide each channel in a separate uncompressed stream - which will generate huge files but has very high quality (HD DVD and BluRay can and do use this option)
So far so good. Next you will need to get all channels in the content out of your
player device. Here you have 3 options:
- Use a digital connection to carry a compressed data stream (AC3, DTS - AAC and WMA output is rare) with all the channels encoded into the stream
- Use a digital HDMI connection to carry each channel in a separate uncompressed stream or carry all channels in a compressed data stream (same as #1)
- Provide one mono analogue connection for each channel
To get multichannel sound into a
receiver or amplifier, the same 3 options are available:
- Digital input of compressed data stream with optical or coaxial cable
- Digital HDMI connection, separate uncompressed streams or same compressed stream as #1
- One mono analogue cable for each channel
This is all very straightforward, especially if you have a compressed stream in your content and want to carry it to the receiver with no alterations. Watching DVD's on a home theater is just that - the receiver decodes a data stream that comes straight from the DVD.
The fun begins when you want or need to convert separate channels into a compressed stream or vice versa. This will always mean encoding or decoding and licensing issues.
With these basics in mind, you can easily see where the possibilities and limitations are for the Apple TV:
- Carrying a compressed AC3 or DTS stream that's present in the content over the optical digital output to the receiver is easy. It's just hauling bits from one end to the other. Playing a DTS encoded WAV file proves that.
- Carrying a compressed AC3 or DTS stream that's present in the content over HDMI depends on whether Apple fully wired its HDMI port and can route the bitstream to that port. If yes, then it's no problem.
- Outputting uncompressed streams over HDMI requires either content with separate streams (unlikely) or content that the Apple TV can decode (AAC should be easy). This puts a strain on the CPU to decode it.
- Outputting a compressed stream in either AC3 or DTS format from uncompressed or differently encoded content (AAC) requires on-the-fly encoding which will need a license and is CPU intensive. Separate hardware is usually required.
- Because the Apple TV has only 2 stereo analogue ports, hooking it up over analogue cable is limited to stereo.
The ALC885 chip in the Apple TV can output 7.1 channels, but only if it gets the connectors to do it. On the AppleTV multichannel analogue is impossible due to the lack of connectors, so the only option for uncompressed multichannel output here is the HDMI port. On-the-fly encoding of a compressed stream seems unlikely to me.
Apple usually pushes standards to their limit, so I wouldn't be surprised if the AppleTV can actually run 8 (7.1) PCM streams over a well-implemented HDMI port. But they will need to decode any compressed format first and you will need a very modern receiver with HDMI inputs to listen to it.
The answer has to come from Apple, as we have no way of knowing what the HDMI port on the Apple TV is actually capable of. Do they list adherence to the HDMI spec anywhere (1.1, 1.2, 1.3)?
The only other option is the USB port. Apple could make a simple USB dongle that provides the necessary analogue outputs, just like the many dongles you can already buy for PC use.
The AppleTV can not convert AAC to AC3, because of a hardware limitation. Go read the first reply to this thread. It is funny, people hear seem to ignore the truth big time when they don't want that answer.
