Usefully, the up/down keys don't change the volume unless the player is also focused.
What's incredibly sad is that j/k/l were agreed upon to rewind/pause/forward the video, and these generally work unless you're in a textbox... but dedicated keys were not similarly approved to control the volume.
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My current winner for Absolutely Favorite Piece Of YouTube-Related Keyboard Functionality©®℠ is...
YouTube Music (https://music.youtube.com/)... which uses a different set of fundamental keyboard shortcuts to YouTube. [;]=pause, [j]=next, [k]=prev, [l]=forward, [h]=rewind.
There are two disasters here.
The first is that <YouTube/pause> == <YouTube Music/rewind to beginning>. "Nooooo! I was 2 hours?? and how many seconds??? into this video... >.<". Naturally, in this situation, I ReWoUnD ThE ViDeO To ThE BeGiNnInG MySeLf, so YouTube's "last play position" indicator can't help me here. YAYYY.
The second disaster is that it's obvious a Vim user clearly argued successfully for Music to use Vi-style hjkl, but both the key choices and how they are presented in the UI could not be less intuitive, regardless of whether the user also uses Vim or not.
I copied above exactly how the UI (in the [?] popup) lists the sequence. Specifically, the whole thing is shifted left by 1 position, wrapping [h] around to the right. Fixing that to show the sequence how a Vim user would expect, it looks like: [h]=rewind, [j]=next, [k]=prev, [l]=forward.
But then, any Vim user is going to be utterly confused by this sequence, not only because of the mild readjustment of assigning up/down to prev/next and left/right to seeking - but because Vim "up" [j] is assigned to "next", and Vim "down" [k] is assigned to "prev".
Upside down playlist much?!?!
I no longer use YouTube Music, solely because of the number of long videos I have rewound and lost my position in.
I'm also incidentally trying to passively commit hjkl to memory (you know, the whole spaced repetition thing), and all the above was just too confusing.
Actually, not quite at the same time, and that returns us to the old question of viability of reinventing GUIs in Javascript. I guess that even around 1990 window messages of some kind appearing with such a delay from a single action would mean the GUI is based on wrong principles, or the programmer doesn't know how to use it.
It's even funnier to imagine what happens when you press and hold space. The button icon is mostly in in-between animation state from all the repeated presses, but the video starts or stops only on first press and on release. Guess how much fun people have programming window system inside a virtual machine inside a browser using window system inside real machine.
j is down and k is up in vim
Edit: I've wondered whether the Dance Dance Revolution on-screen arrow order https://en.wikipedia.org/wiki/Dance_Dance_Revolution#/media/..., which I also have deep in my muscle memory, is somehow also related to the hjkl arrows (as it also goes ← ↓ ↑ → horizontally).
I prefer to be able to set my keys myself. I use the left hand WASD keys together with ctrl+shift for most things so I can control the music in any application (with winamp). No need to find buttons, the hand is already there even if I'm using the mouse with the right hand.
Arrow-up and arrow-down?
I like the context sensitive behavior and wrote a grease mo key script to restore it.
(I don’t know which order the two things happen in, but clearly they should make sure both don’t happen.)
Your browser might try to pop you down half a page if the thing that is selected or highlighted on the page is not the video player itself though. But it works 100% of the time in fullscreen.