There are many different video formats in circulation, including AVI, 3GP, MOV, MPG, WMV and the formats used by DVDs and Blu-ray. One file type that has become a common denominator across multiple platforms is the MP4 file. If you need to convert  a video file to MP4, then HandBrake is an excellent choice. It is a multi-platform, multi-threaded video transcoder that is available not only for Linux but also for OS X and Windows.

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Converting Video Files to H.264 MP4 Format Using HandBrake on Linux (Make Tech Easier)