Hi Xephilas and welcome to the forums! :) There were threads about this earlier. There was someone (can't remember who it was right now) who works professionally with Reaper and had the same problem. IIRC he could workaround this problem by not switching off the audio from the original video, but putting the volume of that audiotrack to -inf. Maybe that helps. If not, try to check the framerates of your project. -Data