Batch Script only converts 1 minute of video -why? (MKV to AVI)

[munster-shug]

Hi folks. I'm trying to get my head around scripting, but most instructions seem to refer to pre-2.6 versions .

I want to batch convert MKV to Xvid AVI and MP3. 
I've found the following script and put it into a .bat file in the same directory as my MKV files.  It runs through all the MKV files and creates AVI files from them, wonderful.

However it only converts the first minute of each 60 min video.  What have I done wrong? Or what do I need to do to fix it?

set avidemux="C:\Program Files\Avidemux 2.6\avidemux.exe"

set videocodec=Xvid

set audiocodec=MP3

for %%f in (*.mkv) do %avidemux% --video-codec %videocodec% --audio-codec %audiocodec% --force-alt-h264 --load "%

%f" --save "%%f.avi" --quit

I am running 2.6 on Windows 7.

Any help would be most appreciated - it is doing my head in!