[MPlayer-users] Questions about spdif/toslink (was: Mplayer/ogm/ogg)

[Robert R. Wal]

On 03.01.02 Arpi pressed the following keys:

> > > btw, why the hell are you encoding to ac3 ?
> > > instead of sending out as 6ch LCPM over sp/dif?
> > 
> > Does it work? Does the standard (whichever aplies here) allow for
> > multichannel PCM sound to be transferred via spdif and do the amplifiers
> > understand and play it correctly?
> > 
> > I mean, I remember seeing several times some bitching and moaning that
> > you can send multichannel AC3/DTS or two channel PCM but not
> > multichannel PCM.
> 
> hmm. dunno about the amplifiers, they may not support it...
> but the standard LPCM header has the space for up to 8 channels:
> 
> //         number of audio channels - 1 (e.g. stereo = 1)         3 bit
> 
> and for other interesting stuff too:
> 
> //         audio sampling frequency (48khz = 0, 96khz = 1)        2 bit
> 
> note that values 2,3 are undefined by std, but they're usually 44100 and
> 32000 hz
> 
> //         audio emphasis on-off                                  1 bit
> //         audio mute on-off                                      1 bit
> 
> //         dynamic range control (0x80 if off)

But what worries me is the speed of spdif/toslink connection.

I was under the impression that this standard was designed for
48kHz/16bit digital audio in times when no one was thinking about the
buffers, headroom for future development etc.

I mean all the digital audio designs from previous era were basically
the digital serial pipe where bits were droping from pipe to the shift
register and as soon as there was 2*16 bit it was sent directly to D/A
converter.

Now 48kHz/16bit stereo is 1536kbps. No digital signal (either DD, DTS or
MPEG audio stream (as seen on some digital satellite tv channels)) I
know of excedes this value. And I haven't seen DVDs with LPCM audio
other than 48kHz 2ch 16bit (but I've seen only two such beasts ;).

So, what is the max speed of spdif transfers, really? Does anyone have
any pointer to good specs, or at least has seen multchannel LPCM tracks
on DVD? And maybe played them succesfully on digital amplituner?

Robert

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