MOV files not streaming in QT on Mac

I’m wondering why some MOV files I try to open online won’t stream in QuickTime. It prompts me to download an additional codec, and the audio will continue playing, but the video will not. I click the link and get taken to the page of third party codecs, but I don’t know which one to install or if it’s supposed to be any of those at all. I don’t have QT Pro, just what came with my computer.

I run OSX and I understand that most people here are on PCs, but after fruitless googling, this site has seemed to be the most likely to help.

Thanks,
M