Emicsoft M4V Converter for Mac is a multi-format video converter. It allows you to convert most video formats into M4V files and M4V files into an array of other formats. The application has quite a few conversion profiles which are supposedly optimized for playback on different devices, including Xbox 360, Playstation 3, AppleTV, iPhone, iPod Touch, etc.
This converter has an awful design. It looks like a Windows application that was transplanted into Mac. The user interface looks a bit old even compared to some of the oldest converters I have seen on Windows. There is a video player for quick video previews and a video editor that allows you to edit videos and add watermarks, trim them and crop them.
In terms of performance, I wasn't impressed at all with this app. I converted an M4V file into two different profiles, one for the AppleTV and one for the iPhone 4, both into different formats. The resulting files didn't have any audio. I tried converting from AVI to MPEG-4 and that worked well.
All in all, this converter might do a good job of converting files, but I know several free ones that can do the same thing, and better.