Thank you! I tried it with another video but couldn't find a comma or anything. Would you tell me where to look on this one? I have another one that looks like this, too.
There are a few ways to pack data into a url. The idea is that the first part of it takes you to the web server, where the server sees the path and cuts off the start and parses some data from it and continues based on that information. (or just records it with the log of the web hit, for metrics or analytics or paying their advertisers etc)
Since there's a few different things they can do (sequentially, or in depth) you sometimes have to peel it apart a bit at a time. First thing to do is break up the parts separated by the initial ? and any & that follow
So you can see this is just a list of posting parameters. Now they're restricted on what they can put in for values due to the limits of URL formats (though seemingly not LENGTH!!) so they encode it. Percents are made for hex values and other times they just block encode chunks of binary data. ei, id, and upn are probably some unique key format. mime is "video/mp4" (because $2F is "/"). There are a lot of 2C (",") in sparams, which is slightly more readable as "clen,dur,ei,gir,id,initcwndbps,ip,ipbits,itag,lmt,mime,mm,mn,ms,mv,pl,ratebypass,requiressl,source,upn,expire". (curiously enough, that's actually a list of the above parameters... interesting!) Signature looks like a hex dump but is strange that it's an odd number of characters. (77)
MANY urls you can just trim off the added junk. For example, if you try to copy a youtube link in most places, you'll get a big mess that starts with "https://www.youtube.com/watch?v=xxxxxxxxxxxxxx" followed by & and a bunch of trash. You can just delete the rest before reposting the link in its much smaller format. You probably don't need the rest, it's usually advertiser tracking. Sometimes it's preferences or settings though, like it may throw you automatically into fullscreen playback or start the video at a specific point etc.