Noticed something strange on YouTube lately in Safari? It doesn't play videos in 4K anymore. We might have the possible explanation as to why.
Safari Lacks Support for VP9 Codec, Therefore You Can't Play Videos Above 1440p
4K has managed to solidify itself as the golden standard for video these days, but Apple on the other hand, is taking a step back. If you open Safari right now, launch YouTube, watch a video, you'll notice you can't view anything in 4K at all. Any given video uploaded in 4K maxes out at 1440p in Safari. Why is that so? Well, the reason behind that is simple, as pointed out by themcfly over at Reddit:
Upon further inspection, I discovered that Youtube stores different kinds of video on their servers, encoded either in VP9 or the older H264 codec. Safari has no VP9 support (at least in my version, still on Safari 9.1 / El Capitan) so it gets automatically served a H264 version from Youtube (you can verify codec by right clicking > stats for nerds). Chrome supports VP9 so gets served that version, but is far more hardware demanding to decode, so I installed another extension called H264fy that served me H264 version on Chrome. So I could use a fully functional Youtube Plus extension in Chrome without my MBP fans lifting off because of VP9.
Basically, Apple's Safari browser on macOS and OS X does not support Google's new VP9 codec for video. Google has put up 4K video in VP9 as standard, but lower resolutions get served up in H.264. If you are a Chrome user, the 4K video you are seeing is powered by the VP9 codec, something which the Big G implemented support for back in 2013 in Chrome. Apple on the other hand, is yet to implement the codec in its browser.
Of course, there is a chance the codec might eventually make its way to Safari in a future update, but we have no clue at all when that might just happen. Right now, if you want to watch anything in 4K, Chrome browser is your best bet. It's absolutely free to download and use.