There are many "recorder" program on (say) osX, which can take the "loopback audio" and video and record it conveniently, why is it so hard to make an "os-level" / "chrome-level" plugin which would allow recording a video on any website? (and not just have to "reverse" the source of the video and download it, like youtube-dl does)
Streams that are not DRM protected can be saved directly by the browser or by free tools like VLC. It would be illegal to try and work around DRM, which is why there aren't easily available tools for that.
Online videos are lossily compressed. If you record them, either you do so losslessly (which will be huge) or you recompress them and lose quality. Plus you have to deal with network buffering, notifications, alarms, etc., not to mention having to wait while you're recording.
If you can download the source video, it's a lot easier.
I agree, but sometimes some videos are not easy to download, in that case it would be helpful to have a means to do an "accelerated, off-screen recording"
