[mythtv-users] AC3, Analog Cable and 5.1

[Michael T. Dean]

On 03/22/2006 06:46 PM, White Joe wrote:
> I found this thread that implies that some NTSC broadcasts may be
> decodable into 5.1 using Dolby Prologic.  Is this true?  Practical?
> Prevalent? Relevant?
> http://www.gossamer-threads.com/lists/mythtv/users/160633?search_string=
> dolby%205.1%20analog;#160633

The part of that thread that I wrote is not completely correct.  
Although the ivtv card doesn't decode the Dolby Surround with ProLogic 
to allow it to encode into a multi-channel format, enough of the 
Surround info should survive recording--assuming you use a sufficient 
audio bitrate--to allow you to decode with ProLogic when playing back 
the recording.  See 
http://www.gossamer-threads.com/lists/mythtv/users/188945#188945

When using Dolby Surround info, your receiver only needs a standard 
stereo input--not the 5.1-channel output from your sound card.  Note, 
also, that the receiver cannot auto-detect Dolby Surround encoding 
passed over an analog output, so you'll need to force ProLogic decoding 
on your receiver.  If you use a digital output, Myth won't encode the 
flags used to indicate Dolby Surround encoding into the stream, so 
you'll still have to force ProLogic decoding.

Mike