Okay, so there are a bunch of different MP4 formats and Mocha is not compatible with all of them. It is a normal production workflow to create lossless or nearly lost less digital intermediates to use in your production. In the long run, it saves time because a digital intermediates or a DI as it is sometimes called, extract faster and render faster than compressed formats. If I'm using Mocha and/or doing a lot of manipulation I always take the time to pull a 10 bit or better lossless DI from any compressed original I have. I suggest you do the same, It will save you a lot of time in the long run.