Let me know if you find any that still don't work.
Great googly-moogly, that was a pain in the ass!
There's a get_video_info that tells you the URLs for the various resolutions of video data of a Youtube clip, in JSON form. Back in 2012, they changed it so that you had to take the provided "sig=" parameter and append it to the video URL before it would work. This signature appears to be a hash of some of the parameters to the URL (similar to what OAuth does) and the video-data URLs give you a 403 without it.
Within the last few months, they've started rolling out a new glitch where sometimes the signature (which is now "s=" instead of "sig=") is tagged with "use_cipher_signature", and... it's enciphered. Just enciphered. No actual crypto: simply a character-position-swapping cipher! These enciphered sigs come in lengths from 82 to 88 bytes, and you have to re-order and drop characters in particular ways to get them down to the 81-byte original signature. Each length seems to have a different algorithm, unless there's an overarching pattern that I haven't spotted.
It's purely security-through-obscurity! What a dick move.
What is this I don't even.
For laughs, check out the decipher_sig() function.
Now I have to wait for Miro to play catch-up and deploy a similar fix. I'm not holding my breath, because they still haven't released even a nightly build that includes the fix for downloading restricted Vimeo videos that I explained to them over a year ago. Sigh.