I have the following problem: 2 video clips with two audio clips. I try to synchronize them with the option "show audio units" to make them perfectly alligned. The problem is, when I select both video and audio, the audio than jumps back to the next frame rate. I lose the exact setting I did when synchronising the files. I did a video to show the problem. Any help would be appreciated.
I think you should try aligning only the audio when you do this. The video tracks have to be aligned to the nearest frame, because video is either showing frame 1 or frame 2 (assuming your sequence frame rate is the same as your footage frame rate).
Audio is sampled at a much higher rate than video. e.g. your video could be 25 frames per second, but your audio could often be 48kHz, so sampled 48,000 times per second.
Your ears can detect very small variations in delay between audio files (of a few milliseconds), and your ear/brain/eye combo can detect very small discrepancies between audio and video lip sync (22ms according to this).