[MPlayer-users] what to pass to -fafmttag option (with -oac copy)

[Good Bad]

I'm trying to copy audio and re-encode video from a 4GB video file. The video plays slow in my computer, so I thought I should reencode it but I want to keep audio quality same.

This is what I tried:

mencoder -ss 00:10:00 -endpos 00:03:00 \
-oac copy \
-ovc lavc -lavcopts vcodec=mpeg4:mbd=2:trell -vf scale=960:540 \
gold.mp4 -o sample.avi

It fails and it says:

Forcing output audio format tag to 0x6134706d.
Audio format 0x6134706d is incompatible with '-oac copy', please try '-oac pcm' instead or use '-fafmttag' to override it.

But is there a way to determine what hexadecimal number to pass to -fafmttag option in this case?

I could settle on -oac mp3lame or -oac lavc, but I want to compare audio quality of m3lame or lavc with the copied sound. (I can't compare with the original video file because it plays so slow)