[mythtv-users] Does SPDIF Input generally work?

[Nick Rout]

On Thu, August 30, 2007 6:06 am, Ken Scales wrote:
> Mitch Gore wrote:
>> On 8/29/07, *Bearcat M. Sandor* <HomeTheater at feline-soul.com
>> <mailto:HomeTheater at feline-soul.com>> wrote:
>>
>>     Folks,
>>
>>     I've been looking all over the wiki for this one and i can't find
>> it.
>>     Provided that i get a sound card that is well supported, will
>>     MythTV record
>>     tv audio  using the spdif input?   Can i expect any problems with
>>     this? It
>>     appears to be just fine, but i'm about to make a purchase of an
>>     m-audio usb
>>     soundcard and it only has spdif in.
>>
>>     Thank you,
>>
>>     Bearcat M. Sandor
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>>
>>
>>
>>
>> i would assume it would work but i have to ask what are you recording
>> that has digital sound and the sound isn't built into the steam as in
>> HDTV recorded via firewire or QAM or antenna.
>>
>> Mitchell
>> ------------------------------------------------------------------------
>>
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>
> I'm not the OP, but one example: my ExpressVu PVR5100 ( = Echostar
> PVR501) records the AC3 soundtrack when transmitted, and plays back with
> s-video and spdif (as well as analogue sound of course).  My older 4700
> receiver also has spdif output.  I'd like to try capturing the spdif and
> mplex-ing it with my video recordings, like Bearcat is proposing, so
> that I could put them onto my much larger Myth storage without losing
> the DD surround. (Aside: yes, I'm familiar with "PVRexplorer", but I'm
> not running Mac or Windows right now.)
>
> I expect some sync issues, but as long as both "tracks" are stable
> timewise (granted, a big hope), adjusting for a time-delay between them
> can be done with available tools (probably manually at first).
>
> So, to echo Bearcat's request, is there a recommended way of setting up
> and capturing spdif audio? (Even something as crude as "cat < /dev/dsp2
>  > filename.ac3" -- to start exploring the possibilities of doing this.)
> It could be an interesting project to work on over the winter months...
>
> Ken.

Fundamentally this doesn't seem any different to using an analogue
framegrabber that presents its audio as line-in or similar. the first step
would be to use alsamixer to set the capture device to be the spdif
source.

This assumes of course that you have a sound card that *has* an spdif
input (as opposed to output).

If you want to play around with some manual muxing of an ac3 soundtrack
into a video stream I recommend avidemux. I regularly convert my stereo
captures to 5.1 ac3 with stereo2surround.sh [1] and mux them back into the
video. Of course I don't get a real 3D soundtrack (trains don't thunder
diagonally through my lounge, you just get noise out of all the speakers)..
Anyway avidemux will happily mux an ac3 soundtrack into an avi.

[1]http://mightylegends.zapto.org/dvd/dvdauthor_howto_surround.html

-- 
Nick Rout