Experience with mencoder

mencoder encodes videos, I use it to encode my DVB recordings. When you run mencoder without any tunning, you will waste useful space. Here is my experience with mencoder:

Removes all black borders
Really !! You can use the filter cropdetect to find the values for the crop filter or use the filter rectangle:

$ mplayer -vf cropdetect video.avi
$ mplayer -vf rectangle=716:428:: video.avi

Avoid odd numbers
as a general advise.

Height and Width
must be a multiple of 16. The video codec encodes the video with 16x16 blocks and if the size isn't a multiple of 16, you will waste space. The filter cropdetect returns values that are a multiple of 16, but also crops the video sometimes to much.

Scale
can help to solve this problem. And sometimes it's better to have a smaller height and width. First just crop only the black borders, then scale the video height and width to a multiple of 16.

For example:

$ mplayer -vf crop=716:428::,scale=640:-10

The new width is 640 and height 352.
The parameter -10 tells the scale filter to calculate the height using the width and to round the height to the closest multiple of 16.

Use filter hqdn3d=2:1:2
Use filter harddup
See man page why

Two Pass Mode
The  first pass analyzing the whole video and writes a statistics file. The second pass reads the statistics file and bases ratecontrol decisions on it. The output file from the first pass can be deleted or send directly to /dev/null

File Size
Should the movie fit on a CD, then you have of calculate the bitrate of your movie:

Bitrate = (Target_Size_in_MB - Audio_Size_in_MB - AVI_overhead_MB) * 1024 * 1024 / Length_in_secs * 8 / 1000

Use the video codec xvid and it will do it for you, you just need to set the video file size in KB (See example).
How to calculate it ? When you use the Two Pass Mode, write down the audio size after the first pass has finished.

Video_Size_MB = Target_Size_in_MB - Audio_Size_in_MB - AVI_overhead_MB
Video_Size_KB = (Target_Size_in_MB - Audio_Size_in_MB - AVI_overhead_MB) * 1024

AVI Overhead
When you use AVI as your container, some MBs will be wasted for the AVI header and index.
For a 350MB file ~ 5MB
For 700MB ~ 8MB

Example

First Pass

$ mencoder -ovc xvid -xvidencopts pass=1:autoaspect:threads=2 -vf crop=715:428::,scale=640:-10,hqdn3d=2:1:2,harddup -oac mp3lame -lameopts aq=3:preset=standard video.mpg -o /dev/null

Second Pass

$ mencoder -ovc xvid -xvidencopts pass=2:bitrate=-595968:autoaspect:threads=2 -vf crop=715:428::,scale=640:-10,hqdn3d=2:1:2,harddup -oac mp3lame -lameopts aq=3:preset=standard video.mpg -o video.avi

Is the value for the bitrate option negativ, it sets the video size in kilobytes [700 (CD) - 110 (audio size) - 8 (AVI overhead) = 580 * 1024 = 595968kb].
The threads option is only useful if you have more than one CPU else remove it.