Depending on the video streaming site the data is most likely automatically being stored in your browsers cache. Usually this data is not easily accessible nor is it easy to piece together.
I highly suggest taking a look at a program such as JDownloader which will find the video sources on pages and allow you to download them in various qualities. Therefore ...
VLC can already do this.
From The Best Hidden Features of VLC:
Find a video on YouTube and copy the URL from the address bar.
In VLC, head to Media > Open Network Stream.
Paste the YouTube link in the box and click Play.
Under Tools, click Codec Information.
In the box that says Location, right-click the block of text and click Select ...
This might help you: https://kwizzu.com/construct.html
Either you merge them together: Merging audio and video using ffmpeg
Or you can use VLC to "watch"/"hear" multiple files at the same time: Watching separate video and audio files
The most advanced solution is to create one video file with multiple audio tracks. This is described here: https://...
This is a result of a bad downloader rather than YouTube throttling.
In DASH (which is what the new tech is called they're now using), a video is not just a single file that gets lobbed your way when you watch it, instead it gets sliced up into small parts a few seconds long each, so things like changing quality and adapting to a changing bandwidth (which ...
YouTube may be throttling its own videos. I can load all their front page material just fine. If I try to load a less viewed video and run it concurrently with a number of front page videos, the front page videos will stream perfectly and the unpopular barely viewed video will stutter and stop while continuing to buffer.
4K Video Downloader is great too. Unfortunately you gotta pay for it. (But you may or may not be able to find cracked versions at "The Bay" =P.)
Copy-paste the video URL into the application and it immediately starts downloading.
You can even copy-paste the URL of a channel/playlist and it will download ALL the videos on that channel/playlist. This is ...
free software for Windows, Mac, Linux
supported by developer
supports various sites, formats, resolutions
grabs links from clipboard
supports pausing download and etc.
p.s: I hope I won't get banned for second answer about it -_-
There is nice Python script called youtube-dl. Usually you can install it straight via apt-get (on Linux) or brew (on OSX).
Or you may try Wondershare AllMyTube which supports video and the whole playlist downloads.