HandBrake is an open source video converter that comes in handy if you're dealing with incompatibility issues between your movies and the media devices or apps you're using for viewing the clips. The program lets you convert videos between multiple formats, supports batch processing, and immediately generates the quality files you need.
You can import as many clips as you like, choose between multiple output profiles, and make adjustments if needed. The utility enables you to crop your videos, select the preferred frame rate and video encoder, rotate them, etc. You can also attach subtitle files to your movies.
In addition, HandBrake comes with a built-in video player which might prove to be of good use if you need to check if the altered clips fit your requirements.
Sadly, the application is missing some features which can be found in other video converters. For instance, it doesn't provide you with an option to trim or extract certain segments from clips. The application also lacks visual effects and the ability to extract soundtracks from movies.
Still, this program is open source, a rare thing when it comes to working with video converters on Macs. So, you should test it if the aforementioned aspects don't mean much to you.