There are lots of video encoders/transcoders available on the internet and most of them are either not up to the mark or quite complex to start with. But, here is a great Open Source project that will just so this right! HandBrake is a free and open source software that is cross platform (works on Windows/Linux as well as Mac OS) video transcoder and it is great!

Supported Sources:

• Any DVD-like source: VIDEO_TS folder, DVD image or real DVD (unencrypted-protection methods including CSS are not supported internally and must be handled externally with third-party software and libraries), and some .VOB and .TS files
• Most any multimedia file it can get libavformat to read and libavcodec to decode.

Outputs:

• File format: MP4 and MKV
• Video: MPEG-4, H.264, or Theora (1 or 2 passes or constant quantizer/rate encoding)
• Audio: AAC, MP3, Vorbis or AC-3 and DTS pass-through (supports encoding of several audio tracks)

Misc features:

• Chapter selection
• Basic subtitle support (burned into the picture)
• Integrated bitrate calculator
• Picture deinterlacing, cropping and scaling
• Grayscale encoding

Download HandBrake for Free from here.