Audio/video run with Cat5e

I've never shared a cable between a phone line and an S-Video, but I can imagine that, due to considerable difference in operating frequencies, you will see no picture degradation. However, it is really worth mentioning that the ring can generate 100V potential on one of the pairs in this cable, so you will feel much safer if you use a whole different cable for your audio/video stuff.

S-video and stereo audio run just fine on CAT5E for just about 100 feet. I haven't tested further without a balun, but if you need to go several hundred feet, you can purchase a couple of baluns (impedance matching transformers) for both ends of that cable, and send the signal without any quality degradation on 500 feet or more.