[Retr0id]

This does not work for sites that serve videos in a segmented format, such as bluesky

[reportgunner]

I downloaded a video off bluesky this way before posting, I didn't check if the whole video got downloaded though, just the extension.

You are right that some websites give you .m3u or some kind of .htm that is not the actual video this way.

[Retr0id]

You presumably downloaded the first TS segment (in MPEG-TS format, not MP4), which could plausibly have been the whole video if it was short enough.

[reportgunner]

It was a very short .webm, looked like a gif converted to .webm

[Retr0id]

Sounds like you downloaded a "gif" embed, rather than a "video" embed. (It's 2024 and everyone serves """gif"""s inside video container formats to save bandwidth, but the UX and implementation details are still different to that of a "video" player)