[mythtv-users] Re: Capturing 5.1 audio
Tony Lill
ajlill at ajlc.waterloo.on.ca
Mon Nov 14 03:06:48 EST 2005
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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