That depends on where you live. In many parts of the world, software patents don’t exist and aren’t applied.

No, e.g. the package x264 from videolan.org is free software (FOSS) with GPL2+ licence.

Never cared. I’m one of those people that would indeed download a car.

Commercial use requires payment to patent holders, free use does not (whenever end user does not pay to watch). I dont know how ad supported streams are categorized, probably commercial. For personal use, I wouldnt worry about the license. Worry when you start a streaming server and start making revenue.