Wow:

   Overview of the control flow (already known):
   The Youtube API provides you with n - your video access token
   If their new changes apply to your client (they do for "web") then it is expected your client will modify n based on internal logic. This logic is inside player...base.js
   n is modified by a cryptic function
   Modified n is sent back to server as proof that we're an official client. If you send n unmodified, the server will eventually throttle you.

So they can always change the function to keep you on your toes, hence you need to be able to run semi-arbitrary JS in order to keep using the API.

Waste of human brainpower but I guess that energy is better spent imagining a world where Google isn't in charge instead of kvetching about what they're doing with their influence.

For those interested further, in some of the past few weeks youtube-dl had stopped working intermittently for multiple hours at a time, and it was precisely related to this code.

We have a custom-made Discord music bot on our server which uses ytdl to stream songs so we can listen together, and at one point we were listening and suddenly got some obscure JavaScript error.

We began joking that there's some bug in the code which breaks it after 6PM, but later found out that Google had changed some of the obfuscated JS and this basically broke this part of code, which prevented us from fetching the song information.

What is interesting is it seems to be constant cat and mouse. I download a YT vid. It crawls. Update yt-dlp, it flies again. I love yt-dlp and use it a lot.

But why not just use a normal JS engine called from Python?

If you start a youtube video and then pause it and resume a few days later, you'll notice that the youtube page plays for ~30 seconds (ie. whats buffered) and then the page refreshes. I'd guess this refresh is to pick up the new javascript and any updates to the HTML code.

It's kinda annoying if you have a lot of youtube tabs open for a long time and come back to them.

> I believe YouTube limits your bitrate if you don't pass a specific calculated value

It's starting to become Widevine bullshit all over again.

It’s not like proof of work at all. It’s just a challenge and response; youtube includes a random number in the webpage for each video, and expects to see a request parameter with a particular value calculated from that random number when you request the video. If you don’t do the arithmetic it throttles you to 50kb/s.

Since the calculation of the response is done in JS, and they occasionally change the formula, some download programs are moving towards running the JS rather than trying to keep up with the changes.

It’s really just bullshit to make people’s lives harder.