[mythtv-users] trandcoding messes up 6 channel audio slow audio playback

Gavin Hurlbut gjhurlbu at gmail.com
Fri Dec 31 10:51:38 UTC 2010

On Fri, Dec 31, 2010 at 1:42 AM, Jean-Yves Avenard <jyavenard at gmail.com> wrote:
> Forgot to say that the mythtv internal downmixer uses Dolby Prologic
> II encoding matrix to downmix ; so when downmixing to stereo, not all
> surround is lost and myth upmixer will mostly be able to output the
> original stream.

Nice.  Yes, I can attest that it does sound pretty good too.

> for 5.1 -> stereo, it's about
> L = L + (C - 3dB) + LS * sqrt(2/3) + RS * -sqrt(1/3)
> R = R + (C - 3dB) + LS * -sqrt(1/3) + RS * sqrt(2/3)

Hmm, I didn't realize there was the crossover from the rear channels.
I should find some time to play with that in the sox implementation
this weekend.  Not sure if it likes negative coefficients though, but
cool.  Of course, I'd still rather do the downmixing (and upmixing
should we need it) right in mythtranscode, using the same exact code
as it does for playback.  Over time, the general wish is to absorb all
of nuvexport into mythtranscode somehow.  No real roadmap for it yet,
of course :)

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