I have made some visuals with Videosync for all ten tracks on my debut album and have arranged them in a dedicated Ableton session such that such that they seamlessly blend into each other as the album progresses. Everything works perfectly until I try to save the video via Syphon Recorder. On a couple of tracks, the video doesn’t fill the screen. I’m sure it’s something really simple but I just can’t figure it out.
Hello there and welcome to the forum! If you go to the Settings window
of Videosync, is the Resolution set to “Same As Window”? If yes, I recommend setting it to a fixed value (like 1920x1080 or 1280x720). If no, do let me know 
Hi Jean-Paul. It worked. I really appreciate your help. Thank you!
I have a new problem. I’ve exported the audio separately and then combined it with the video in iMovie. I’ve aligned both on my first song, but they start to go noticeably out of sync by the time it reaches song three. By song ten the video is lagging by around three seconds.
Happy to help Are you using an MP3 render or a full quality WAV when putting them together in iMovie? This might make a difference.
You can also consider starting a new Live Set, and drag only the audio WAV and the recorded video file onto two tracks in Arrangement View, and use Live’s own video engine to render them together. This way you can also Warp the recorded video file to better match the audio, albeit as a last resort.