> they even go out of their way to seperate audio and video requests
Just to give them the benefit of the doubt, many video sites do this (YT being the biggest). It allows you to change the video source on the fly (changing the bitrate for example) without effecting the audio playback so preventing any audio glitches during the swap. People are a lot more forgiving of video artifacts then they are of audio glitches. It also allows you to have a lower bitrate copy of the original video for mobile playback without having duplicate copies of the audio.
So maybe thats why they do it and not some evil plan to annoy you from saving the video (Tools like youtube-dl will happily merge the video and audio into a single container after downloading both pieces of the puzzle).
Although, I don't use reddit anymore, I gave it up a few years ago, so maybe they have gone completely evil and the video/video track splitting is simply to annoy hotlinkers (I know they have been throwing more and more dark patterns in to their redesign, the redesign was basically the kick I needed to quit that habbit). Just giving them the benefit of the doubt on that one for now as there are legit reasons to do it.
EDIT: 1) My ref to youtube-dl is about how it will merge the 2 after giving it a single YT URL. No idea if it works on reddit, but as it works on a number of sites I wouldn't be surprised if it also works on reddit (its been years since I've been on reddit in any meaningful way, so never had the urge to try).
2) ffmpeg and avconv will merge pretty much any audio track with any video track you throw at it into a single container without the need re-encode the video. In fact iirc I think those are the tools youtube-dl will use to merge the tracks after downloading content from YT.
3) as for annoying hotlinkers, there are (imo) better ways to annoy hotlinkers then spliting the audio/video tracks. Personally my fav way is to replace the video being served to the client with a copy of Never Gonna Give You Up serverside after the hotlinking is detected - but serving the orig video when its not hotlinked, but I'm a dick :-P (a more sane and polite way would be to simpy not serve any video at all, saves wasting bandwidth).