Conversion software

Handbrake is a reputable app. If you download it from the developer site, you don't have to worry about it including malware.

Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 12 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided by practicing safe computing (see below). 3rd party antivirus apps are not necessary to keep a Mac malware-free, as long as a user practices safe computing, as described in the following link.

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Read the What security steps should I take? section of the Mac Virus/Malware FAQ for tips on practicing safe computing.

 

I use it for quick editing of videos (like cutting out commercials). But I'd recommend Handbrake for format conversion.

 

Handbrake is free and does an excellent job.

Just be aware that conversion will usually degrade the video. Not noticeably if the original is high quality.