[MEncoder-users] problem re-encoding 5.1 audio ... channels get mixed up

[n0dalus]

On 1/14/06, Phil P <phil at payneinthe.com> 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?

livavcodec does this when re-encoding 5.1 sound. It's been discussed
before. I can't remember why nothing was done about it.

> Is there any workaround?

-af channels=6:6:0:0:4:1:1:2:2:3:3:4:5:5

That should be work.

> 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,
n0dalus.