How to convert video files for Creative Zen X-Fi with freeware mencoder(command line)

What is Creative Zen X-Fi
Creative Zen X-Fi is a portable music player. It supports MP3, WMA, AAC5, WAV (ADPCM), Audible 2, 3, 4 audio formats; MJPEG, WMV, MPEG-4 video (including DivX and XviD); and JPEG photo formats.

How to convert video files for Creative Zen X-Fi from the command line (terminal)
The following command allows to convert intput.avi to output.avi using Xvid (MPEG-4) video codec and MP3 Lame audio codec.

mencoder input.avi -o output.avi -vf scale=320:240 -oac mp3lame -ovc xvid -xvidencopts bitrate=800

The above mentioned command assumes that the aspect ratio of your video input.avi is 4:3. If you have a different aspect ratio, such as 16:9 (the format of most widescreen videos) you will need to know the horizontal and vertical resolution of the input video. You can find it out with an FLV player like freeware VLC player.

Creative Zen X-Fi is very picky about the resolution. Make sure to convert to 320x240 (unless your player supports better resolution)

If you want to convert 720x416 video then convert it to 320x something. Divide 320 (new horizontal resolution) by 720 (old horizontal resolution) and you will get 0.444444444. Then multiply
416 (old vertical resolution) by the above mentioned ratio (416 by 0.444444444). Because the resolution should be divisible by 16, you can use either 320x180 or 320x196.

We will use 320x196 and then add the "-vf-add expand=:240" switch to get 320x240 video resolution in output.avi:

mencoder input.avi -o output.avi -vf scale=320:196 -vf-add expand=:240 -oac mp3lame -ovc xvid -xvidencopts bitrate=800

How to convert all FLV files from the current directory and all subdirectories to Creative Zen .AVI files (Linux)

find ./ -name '*.flv' -type f -exec mencoder {} -o {}.avi -vf scale=320:240 -oac mp3lame -ovc xvid -xvidencopts bitrate=800 \;