SMPlayer v0.8.0 using mplayer 2 v2.0-554-gf63dbad
Debian Testing (Wheezy), Linux 3.2.0-2-amd64 #1 SMP Fri Jun 1 17:49:08 UTC 2012 x86_64 GNU/Linux
In order to passthrough non DD5.1/DTS multichannel audio to my surround sound system, I transcode such audio to AC-3 via the following mplayer argument:
When 'lavcac3enc=1:640' is placed in 'Audio filters' of Preferences -> Advanced -> Options for MPlayer, nothing happens - according to the MPlayer log, 'lavcac3enc=1:640' hasnt been passed to it in any form.
When you add '-af lavcac3enc=1:640' to 'Options', it works.
Kudos to making a program so flexible that when it breaks you can still use it to workaround the problem :)