How to Compress a video using Virtual Dub
Compressing and encoding High Quality Video Using Vdub:
We have recorded the video at 6 Mbits (6000Kbps). With the help of DivX we can compress it to 1500kbps without affecting quality.
1. Remember to keep the settings we kept for TV Caps. For compressing High quality Videos u can use either DivX or Xvid codec. I prefer Divx as we are dealing with TV recorded Videos which need more workout.
2. Go to Video > Compression > Select DivX > Click Configure.
3. In Main tab > Keep Certification Profile as Unconstrained > in Bitrate > 1-pass & keep value as 1500kbps.
4. In Codec Tab > keep settings as INSANE Quality. This is MOST Important, Dont change this!!
5. In Video tab > u can keep settings as per ur preference but Do not increase the resolution of ur image. Now u can come out of DivX settings.
6. In Audio Tab > Select Full Processing Mode > Then Select Compression > MPEG LAYER - 3 > and keep 24kBits/s mono for normal video and 56kBits sterio for a video which contains music 
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NOTE : Selecting INSANE Quality option is going to take hell lot of time so be patient. If u r in hurry u can select any of the other options but that is gonna affect quality. In Audio Compression You can select NO Compression as well, but that is gonna make file size bigger
courtesy : desitorrents