And what video files are you actually trying to use? You left out the most important info. mocha is very picky about what it supports.
Read the Mocha help for what kind of formats (and codecs) it can support.
Take your original footage and load it into the Adobe Media Encoder. Pick any of these presets:
CC Media Encoder:
Then just spin down your choice, select the frame rate and size that matches your video, render, and replace the footage with the image sequence you generate.
Create a new After Effects from your footage, add the new footage to the Render Cue and use the default Uncompressed preset in the output module OR make your own new preset using QuickTime Photo Jpeg or Motion jpeg with quality set to 90% or better. You can use most viable production codecs without problems. Image sequences always work in Mocha IF YOU MATCH THE ORIGINAL FOOTAGE and the COMPOSITION Frame Rate! Video in a suitable codec always works under the same rules. The footage frame rate and frame size and the comp frame rate and frame size must match.