[MEncoder-users] One more problem with audio when joining two files

[Apple7777]

When I try to encode videos to MPEG4 first:

mencoder -vf scale=448:-3,expand=448:336 -sws 9 -ovc lavc -lavcopts
vcodec=mpeg4:vbitrate=4000 -frames 1000 -oac mp3lame -lameopts cbr:br=320:mode=3
-channels 1 -o test2.avi test07g.avi

mencoder -vf scale=448:-3,expand=448:336 -sws 9 -ovc lavc -lavcopts
vcodec=mpeg4:vbitrate=4000 -oac mp3lame -lameopts cbr:br=320:mode=3 -channels 1
-o test1.avi logo7aaa.avi


And then join them:

mencoder -ovc copy -oac copy -o test.avi test1.avi test2.avi

OR

avimerge -o test.avi -i test1.avi test2.avi


I get video with about 1 second audio delay. When I encode files separately,
there is no any delay there.

I wonder, is this a bug or I use wrong commands?