[mythtv] Internal DVD Player multichannel support

matt mead m-mythtv at goof.com
Tue May 2 12:57:11 UTC 2006

Steven Adeff 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.

I don't know how faithful it is to what an embedded DPL/DPLII decoder would 
produce, but there is this for upmix to 5.1:


It might be a good starting point for taking a stereo audio track and 
outputting it to 5.1.  To switch to "bypass" (stereo only) we'd still need to 
perform high-pass filter, low-pass filter and steer the highs to the front L+R 
and the lows to the LFE.  It would be nice to have configurable frequency 
cutoffs for the HPF and LPF.

I'll try to devote some time to getting the patch running locally and then work 
on support for some of this stuff.  I can work against .19-fixes branch on a 
gaming system with a 5.1 PC speaker setup for testing.

This is all probably a "corner case."  My guess is most people will have an 
onboard AC3 decoder they can just dump to with passthru.


matt mead


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