[MEncoder-users] Downmixing and normalising

[Corey Hickey]

Olivier Rolland wrote:
> Hi,
> 
> I want to encode a 5.1 DVD in a stereo avi with audio normalised. What
> is the best ways to get that:
> 
> -channels 2 -af volnorm
> or -channels 2 -af channels=2,volnorm
> or -channels 2 -af volnorm=2,channels ?
> 
> Can I omit "-channels 2" ? What is the precedence between -channels and -af ?

I could say that -channels has higher precedence, but that might be
misleading by way of lack of information, so:

"-channels" requests that the audio decoder provide that many channels
of output. Note that "request" is the operative word. Some decoders
won't downmix and (as far as I know), none of them upmix.

"-af channels" is a filter for changing channel layout and possibly
emitting a different number of channels. As a filter, af_channels has no
control over the number of channels it receives, though you can
configure af_channels to ignore channels you don't want.


Specifically for your case, you only need to use "-af volnorm", since
"-channels 2" is the default.

-Corey