SPDIF and 24bit audio

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Hi,

I have a number of 24bit 96kHz files. My hardware platform is an Nvidia 
Ion based system and I am connecting to an external DAC via SPDIF. The 
Ion platform claims to be using a realtek ALC662 device to output over 
SPDIF. Looking at the 662 datasheet, it says the following "The ALC662 
series support 16/20/24-bit SPDIF output function and a sampling rate of 
up to 96kHz".

In xbmc, I have selected the custom audio output and the value is set to 
"hw:0,1" (the SPDIF port).

Turning debugging on in xbmc and the system sees the file as 24/96.

WAVCodec::Init - Sample Rate: 96000, Bits Per Sample: 24, Channels: 2

but the ALSA initialise initialises to 16 bit:

CALSADirectSound::CALSADirectSound - Channels: 2 - SampleRate: 96000 - 
SampleBit: 16 - Resample false - Codec  - IsMusic true - IsPassthrough 
false - audioDevice: hw:0,1

Looking at the hardware params:

root@xbmc:~# cat /proc/asound/card0/pcm1p/sub0/hw_params
access: RW_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
rate: 96000 (96000/1)
period_size: 4096
buffer_size: 16384

The question is: what happens to the 24bit audio? Am I getting full 
24bit out of the SPDIF port or is it being down converted to 16bit? If 
it isn't 24bit, is there any way for me to force it to use 24 bit (the 
device is S16_LE and S32_LE capable but surprisingly doesn't support 
S24_LE). Is this a bug in xbmc?

I'm running ALSA v 1.0.20 but I can't find any mention of related 
changes here in the upgrade logs on the ALSA wiki.

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