[MEncoder-users] problem re-encoding 5.1 audio ... channels getmixed up
Nico Sabbi
nsabbi at email.it
Fri Jan 13 14:51:33 CET 2006
Phil P wrote:
> Hi,
>
> I have a file with 5.1 audio that I want to re-encode as 5.1,
> basically so I can apply the "volnorm" filter and raise the sound level.
>
> I use the following command:
> mencoder <input-file> -ovc lavc -oac lavc -lavcopts
> acodec=ac3:abitrate=448:vbitrate=1350:vpass=1 -ffourcc DIVX -channels
> 6 -af volnorm -o <output-file>
>
> The command completes correctly but when I play the file on my 5.1
> speakers I find the channel outputs have been transposed ie. the
> original file plays fine but when playing my re-encoded file the
> centre channel appears to be front-right, front-right is now
> rear-right... etc...
>
> As I'm not applying any channel filters I wouldn't have expected this
> to happen.
>
> Does anyone know why this occurs?
> Is it a common problem?
it sounds like an unlikely bug to me (volnorm shouldn't change the
channel mapping,
but I can barely believe it does it). Anyway, re-compressing sound after
having normalized
volume was always considered a bad practice by people more aware of
audio processing
than me
> Is there any workaround?
-af volnorm,pan=.... (but it's not so easy to use)
> Is there an alternative method to normalize the volume on the original
> stream?
>
> I've searched the archive and couldn't locate a similar question.
>
> Much thanks,
> Phil.
>
good luck
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