Each time I Cmd+S an .mp3 or .mp4 file, it saves it, but as it turns out, as an empty Zero bytes file. Even if I'm explicitly choosing Save As and Format=Page Source, it doesn't work. I doubt this is an expected behaviour as it has let me down several times since some of the files are no longer online.
This issue is very similar to After Maverick, Safari will not download PDF files, but the solution there doesn't work for me as I don't even have that "Allow Plugins" checkbox in my version, nor do I use any.
I have Safari 11.0.3 on Mac OS Sierra 10.12.6
This is very frustrating. Please help
Got the same problem again, googled my own question.
As it turns out, where exactly you right-click makes a difference. I happened to be doing it on a progress bar, and that gave me the "Save Page As" option, which results in zero-bytes downloads. However, if you right-click the timer or the controls, it gives you a whole other dropdown with some media-related options, one of them being Download Video As, which works properly.
So the answer is: