Now that a certain popular video hosting site has gone html5, it now keeps video files and their respective audio tracks separate. I noticed this while trying to find a way to get the site to stream *only* the file to my browser without loading the player interface, recommended videos, etc..
One well-known method for pulling video from that site is to simply dump its URL into VLC as a media stream. (Sometimes you have to remove the "s" from "https." And sometimes it doesn't start converting the video unless you open the Messages dialog- don't ask me why.)
I've found another method using the browser- but the catch is that you only get the .webm file. So you'll have to convert it after. I will describe the Firefox method because that's what I used.
1. Go to video page and let part of the video load. Play a couple seconds of it.
2. Right-click on the page and select "inspect element."
3. In the window that pops up, go to the "network" tab.
4. In the subtab below it, click the "media" tab. You should see a series of files of type "webm" with file names that start with "videoplayback?"
5. Click on a random entry. In the right-hand window next to this one, make sure "headers" is selected. In the "Response Headers" section below it, look for the header that says "content-type." This will tell you whether the link you have clicked is for audio or video.
6. If this is the respective stream you want, right-click on the filename and "copy url."
7. Paste the URL into a new browser tab, but do not hit enter yet! Find the text string in the url that says "&range=" and delete it all the way up to before the next "&" symbol. If you do not do this, it will restrict the length of the file you are about to load!
8. Once you've trimmed the URL, hit enter. It should load the video or audio file in your browser as a .webm. Now you can "save as" to wherever you want.
This method is obviously more involved than the VLC method, and it only gives you video OR audio at a time, but it's a fun little workaround. I'm sure there are more parameters in the URL that you can adjust, but I'm too lazy so you'll have to figure that out on your own!