[mythtv-users] Re: Capturing 5.1 audio

[Tony Lill]

Been looking into this myself. Basically, you need a soundcard that can
record the AC-3 signal from coax, and you need a video capture device
that does NOT encode audio into the datastream you get from
/dev/video. This is basically anything except the PVR-XXX cards. And of
course, you need some way to get the AC-3 datastream to your
receiver. Make sure that someone's actually gotten recording under
linux to work before you shell out your money. From what I've read, it
can be a bit tricky.

I've got an amd64 motherboard that has digital coax in and out (using
the nforce4 chipset). As soon as I verify that it can capture an AC-3
datastream under linux, I'm thinking of grabbing some bttv supported
card cheap off e-bay, or maybe a Matrox Marvel G200, if it will work
on the amd64.
--
Tony Lill,                         Tony.Lill at AJLC.Waterloo.ON.CA
President, A. J. Lill Consultants        fax/data (519) 650 3571
539 Grand Valley Dr., Cambridge, Ont. N3H 2S2     (519) 241 2461
--------------- http://www.ajlc.waterloo.on.ca/ ----------------
"Welcome to All Things UNIX, where if it's not UNIX, it's CRAP!"

John DiLorenzo <jdilorenzo at gmail.com> writes:

> OK, so I'm out of luck recording the audio with the PVR-150.  How about the sound card method... Will I be able to use a single soundcard to capture 5.1 via coax, and then
> output via optical?  Will I need 2 soundcards in this box?
>
>
> On 11/12/05, Michael T. Dean <mtdean at thirdcontact.com> wrote:
>
>                PVR-150 records NTSC or PAL.
>      
>      NTSC/PAL don't do 5.1 channel audio--they support only 2-channel stereo
>      sound.
>      
>      Therefore, PVR-150 cannot record 5.1 channel audio.
>      
>      However, Dolby Surround ( http://en.wikipedia.org/wiki/Dolby_Surround )
>      is a technology whereby multiple audio channels ( 4.0 channels) are
>      encoded within a standard 2-channel (stereo) signal and decoded using a
>      Dolby Pro Logic ( http://en.wikipedia.org/wiki/Dolby_Pro_Logic )
>      decoder.  Often, when a show is broadcast (on digital stations) in Dolby
>      Digital=AC-3=5.1 ( http://en.wikipedia.org/wiki/Dolby_Digital ), the
>      analog stations transmit Dolby Surround encoded in the stereo signal.
>      
>      The PVR-150 records the stereo signal broadcast with the show, so--in
>      theory--it would be possible for Hauppauge to support Dolby Surround.
>      However, the PVR-x50's do not contain a Dolby Surround decoder--instead
>      only a stereo decoder--so only two channels of audio are encoded in the
>      stream.
>      
>      However, most ALSA drivers will automatically replicate the left- and
>      right-front channels to the left- and right-rear (and surround if you
>      have a 7.1 channel setup) speakers since it has only a minor effect on
>      the perceived positionality of the sounds.  If your driver doesn't, you
>      can easily add a translation table to your .asoundrc to do it yourself.
>      
>      If you really want 5.1 channel, though, you'll have to go to a digital
>      video broadcast technology (like HDTV (US) or DVB).
>      
>      Mike
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>
>
>
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