Any Video Converter - Converts most videos to any format you want.
http://www.any-video-converter.com/download-avc-free.php

VOB2MPG - Losslessly converts .vob to .mpg.
http://www.videohelp.com/tools/VOB2MPG
Or you can just change the .vob extension to .mpg

To cut chapters from a DVD, use DVD Shrink.
http://www.videohelp.com/tools/DVD_Shrink
http://forum.videohelp.com/threads/296328-How-to-cut-out-clips-from-DVDs-and-convert-to-AVI-MP4-using-free-software

To convert DVD to mp4 or mkv, use Handbrake.
http://www.videohelp.com/tools/HandBrake
http://www.dvd-guides.com/guides/dvdrip/235-convert-dvd-to-h264-mkv-mp4-using-handbrake

Use ImgTools Classic to convert Video_TS folder to .iso image.
http://www.videohelp.com/tools/ImgTools

To cut mkv files keeping the original quality of the video, use MKVtoolnix
http://www.videohelp.com/tools/MKVtoolnix
1. Install MKVtoolnix
2. Add your video file.
3. Go to Global -> enable splitting -> after timecodes.
4. enter the timecodes of the part you want to cut, e.g. if you want to cut from the 86th minute to the 90th minute, format will be:   01:26:00,01:30:00
5. Start muxing
6. Several files will appear when muxing is done, just delete the ones you don't need.

To convert from aac to mp3, demux using tsmuxer and convert using lamexp.

To convert vob to mp3,
1. Use dvd shrink to cut the chapter you want.
2. Use DGIndex to demux the file. http://www.videohelp.com/tools/DGMPGDec
3. Convert the audio file to mp3 using lamexp.

To convert m4v to mp4, simply changing the file extension may sometimes work.
To cut out parts of a mp4 file, use Avidemux
http://www.videohelp.com/tools/AviDemux
1. Add your video file.
2. Use the slider to choose the starting point of where you want to cut.
3. Press the 'A' symbol
4. Choose MP4 format, and save the video.

To hardcode .ass subtitle files to an mkv file, use Handbrake.
Simply open up the mkv file in handbrake, go to the Subtitles tab, click add, and check the 'Burn in' option.

To convert .mpa to .mp3, use audacity. import the file, then click 'export selection as'.

To rotate and save a video, use avidemux.
Video -> Filters -> Rotate
Don't use Video Output as 'Copy'. Choose something else, e.g. Mpeg4 AVC (x264), and therefore use Output Format -> MP4 Muxer.
File -> save