Other mistake: When the Libyans shoot at Doc Brown and the bullets hit his van they leave no bullet holes, just impact sparks. (00:29:10)
Other mistake: When young George and Marty are in the backyard talking about what will happen at the dance, young George hangs up clothes to let them dry, but if you look closely the clothes are actually already dry.
Answer: Video tape system back then could output an NTSC video signal, just like broadcast at the time, and up to HD in the 2000s. Usually there was a switch on the video device to change the output frequency between channels 3 or 4. Depending on what was an open channel in your area.