Try Bigasoft ProRes converter and see if it works for you, they offer a free trial.
"Bigasoft ProRes Converter converts video in any format like MKV, MTS, MOV, MP4, WMV, AVCHD, WebM, RMVB to lossy video compression format ProRes 422, ProRes 4444, Apple ProRes 422 (HQ) for import and edit in FCP and FCP X."
All the converters are basically GUI for the OS built in code/process, so they work about the same on pristine well behaved video. There are several GUIs in the app store.
Bigasoft seems to be more reliable than anything else I've tried, free or otherwise, and I've tried them all. If Bigasoft can't work with the video, well, you are into pro/lab level manipulation. Where others stall, this software just seems to just work its magic. Its not infallible, but if you know what you are doing, the software allows access to plenty of customizations and parameters to tweak away at.
Even at $30, less with coupons, not a bad price for what you get.
I've converted tons of MTS and WMV videos with it. Does a nice job.