[mythtv] Internal DVD Player multichannel support

[Ed Wildgoose]

Hi

> I assume you are talking about my patch #1104.
>   

Nope, I hadn't spotted that.  Will investigate further! 

> AC3 and DTS both have downmixing support built in. just need to specify the 
> number of channels when decoding. also supports upmixing for 2 -> 6 channel 
> synthesised but not sure on this. still dont have a 6 channel system to 
> listen/test with. there is no generic downmixing component in libavcodec 
> though you could use liba52 or dts directly but the format is not 
> interleaved. not sure why you would want to do this outside of the decode 
> operation anyway.
>   

There is no reason other than it's easy to get downmixing wrong.  You 
need to chop stuff around and it's often useful to drop channels 3dB to 
prevent overload, also bass management can be problematic going from a 6 
channel system to a 2.1.  In my case I have a "4.1" system, ie no center 
- but actually I fake this by spitting out a 6 channel signal and 
downmixing using my own filters in Brutefir.

> what I wanted to do was incorporate some way of the audio layer handling any 
> number of source channels without being explicitly configured for them. 
> output channels (analog) I thought just limit to 2 and 6 which alsa can 
> handle.
>   

Not sure what you mean?  You can just throw away extra data, or ask the 
sound driver how many channels it think it has (which may be wrong, but 
at least if the card says it has 2 channels then you can be sure there 
is no point sending 6 to it!)

I think it's worth trying to design for the full range of options though 
or it will come back to kick you later.  Bass management is the bugger, 
so best to see if it can be handled by avcodec, otherwise need to steal 
some filtering from mplayer (has some high speed and high quality 
options available through libavc)

I'm keen to try hacking something together at this stage to see what's 
possible and as you say we can work at it from the position of having 
limited supported speaker arrangements and work back from there.

Will be in touch once I have played with your patch

Cheers

Ed W