[mythtv] Internal DVD Player multichannel support

[Steven Adeff]

On 5/2/06, Steven Adeff <adeffs.mythtv at gmail.com> wrote:
> On 5/2/06, matt mead <m-mythtv at goof.com> wrote:
> > Mark Spieth wrote:
> > > I havent heard of DPL/DPLII. I dont think there is a decoder in lavc. could
> > > be wrong of course.
> > > AFAIK the only multichannel decoders present are AC3 and DTS.
> >
> > Dolby Pro-Logic (matrix surround encoded into stereo audio) and Dolby Pro-Logic
> > II (a similar concept, though I'm not as familiar with it).
>
> I was not able to find any GPL'd code for this in my quick google
> search. I do know that its some basic math and there are a few
> documents on the web that discuss the math. I don't know whether thats
> enough for someone to throw a DPL/DPLII decoder library together or
> not though. I'll keep digging further to see if I can find any DPL
> code thats OSS and collect what documents I find on the matrix math.

per usual I speak too soon. AC3Filter, a AC3 codec for "that other
OS", appears to do  "DolbySurround/ProLogic/ProLogicII downmixing".
Which converts AC3 into a DPL stereo signal. I assume the code could
be "reversed" to extract discrete channels from a DPL stereo stream.
http://ac3filter.sourceforge.net/

Though I can see how those with non-AC3 receivers may like to have AC3
converted to DPL for 5.1 channels that don't carry a secondary stereo
audio stream.

Dolby Pro Logic II explained
http://www.dolby.com/consumer/technology/prologic_II.html

DPLIIx explained
http://www.hometheaterhifi.com/volume_11_1/feature-prologic-iix-3-2004.html

Some logic
http://www.hometheaterhifi.com/volume_8_1/dolby-prologic2-3-2001.html