[MEncoder-users] ac3 channel mapping

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Rolf Ernst <rolf.ernst at silverlightning.org> wrote in
news:BANLkTinTcGAa8VcDDTuijE71TOWKFBxM=w at mail.gmail.com: 

> Googled and googled but couldn't find the info or syntax for the
> channel mapping:
> 
> I have ac3 audio in my input file and just want to downsample the
> bitrate, essentially leave the channel mapping in place. First of
> all, mencoder is a bit confused and thinks it is 2 channel but
> mediainfo clearly says six channels. That aside, I let it guess
> the channel assignments but it clearly gets it wrong. Mediainfo
> says that this is my channel assignment: Front: L C R, Side: L R,
> LFE (of course, I do not know whether this is correct but 
> generally pretty reliable). What do I have to specify for
> -channels? Or do I specify -pan? Anyhow, how do I get the channel
> assignment right? 
> 

This chart with suggested mapping commands should help.
"Understanding Channel Arrangements for 5.1 Audio Formats"
http://wiki.flexion.org/ConvertingMKV.html#7.2