Depending on the VCR it will tear from visually nothing to really bad. Laser Disk players (and I think DVD as well, though its funny, I dont think I ever fed a DVD input into my flyer) will sync fine, you may have to reboot to get it in sync. Cable tv (and probably from an antennae) sync as well. Most pro decks have a TBC, I used to feed everything in via my Hi-8 deck and never had a problem because of that. In actuality TBCs for an amiga are really cheap these days, I've seen them go for less then $100 on Ebay. If you want more then 1 channel, there are several 2 channel TBCs or just get 2 single channel ones. Any other questions about Toasters, I dont mind answering at all.
-Tig
