Capturing 5.1 audio from SPDIF

[Caple]

Hi there.
I have a friend who bought a new mobo and is trying to capture 5.1 audio using the SPDIF input (at least that's what he told me).
He is using iuVCR to capture at 720x480, setting the audio input as SPDIF, using a Sky digital signal with svideo and spdif outputs from his STB.
He always have wav audio and he said the only option to choose on the audio tab is PCM.
Does anyone know how he can capture 5.1 audio with iuVCR? Does he need any plugin or something like that?
Or maybe you guys suggest another software.
His capture card is a Pixelview PlayTV Pro.
Thanx.

[Cornucopia]

The "SPDIF" protocol is actually a strictly 2channel protocol, meaning stereo PCM is the max that it will support (48kHz, 20bit--IIRC).
However, the ports can be "Coaxial" or "Optical" and may support other protocols/streams.

Often, DVD players have setup menu choices to allow for 5.1 DTS or AC3 signal to be sent out through these ports, and the choices are usually: "PCM" (aka downmixed to stereo LPCM on SPDIF) or "RAW" (stream left as is, but buffered to SPDIF-default data rates) or "None" (nothing goes out).

It'll have to be figured out whether your tuner/receiver supports these options (specifically RAW), otherwise you're stuck with the 2 channel only for this setup.

Scott

[Kurt S]

"The "SPDIF" protocol is actually a strictly 2 channel protocol"

Am I missing someting here? I run a spdif connection from my DVD player to my receiver and get full DTS 5.1 and Dolby Digital 5.1 through it.

[Cornucopia]

Yeah, so do I (same setup as yours). That's why I stated the "RAW" stream setting works for 5.1. But it's not strictly a SPDIF protocol then, it's just a buffered raw (as in demuxed but un-decoded or unconverted) stream sent out over the Digital port (whether RCA "SPDIF" coax or "TosLink" optical).

It's kinda like DV over Firewire vs. HDV (or some other data stream or network protocol) over Firewire. Firewire/1394 is the port and the wire and link protocols, and DV was made with that in mind (or vice versa), but it can also be considered a generic serial data transfer connector (just like USB is), which can make it more agnostic to the type of stream being sent down it. However, with non-default stream types come some incompatibilities.

Scott

[Cornucopia]

BTW, I'm saying this -may- be possible if your system can output the RAW stream. There's still the matter of your capture/firewire card being able to support (and decode/recognize) the RAW stream coming in...

Scott

[Caple]

The sound that comes from the STB is directly connected to the input on the motherboard. My friend is able to receive the 5.1 sound.
The problem is, maybe, with iuVCR. He can't choose other record option than PCM.
That's why he needs to know if a plugin is needed or maybe another software.
BTW, thanx for the explanations, Cornucopia and Kurt S.

[Nelson37]

SFAIK, the only way this can be done is with a sound card that can capture 24-bit audio, and is bit-accurate. The captured AC-3 stream is then run thru BeSplice to remove timing gaps. Capture is done at 48k PCM stereo, IIRC. What you are actually capturing is the raw AC-3 data stream, undecoded.

There is more info over at Doom9 about this, I personally have never had the correct hardware to attempt it.

[Kurt S]

Ok that makes sense. Thanks for clearing that up Cornucopia.