Download YouTube videos. Video formats are listed at the top of the watch page. Video links are tagged so that they can be downloaded easily.
Hi, the file extension is controlled by the browser. You should be able to enter the extension manually if it is not added.
Videos save with no extension
Just tried out your script in safari using Tampermonkey on the video and if I try to save the M4V version it downloads the video with no extension. If I try to download the MP4 version, the extension is properly added. The video I tried this with is added. https://www.youtube.com/watch?v=T0YHCywNRbE