Linux developer Hector Martin has discovered that YouTube is "deliberately crippling Firefox on Asahi Linux." Martin, also known by the handle Marcan, says YouTube downgrades the video quality and resolutions served to Firefox users on Macs with Arm-based systems, at least when they're not running MacOS. This behavior is particularly galling as Arm-devices can be very powerful in 2023. Asahi Linux, for example, is a project responsible for porting “a polished Linux experience” to Apple Silicon (Arm CPU architecture) Macs.
Marcan confirmed his YouTube downgrade on Arm hunch by changing the browser user agent (UA) and doing some A/B testing. After changing the Firefox UA parameters from ‘aarch64’ to ‘x86_64’ he says "suddenly you get 4K and everything!"
Digging a little deeper, Marcan checked the code that was responsible for the Arm reaction. He noted that YouTube would serve 1080p videos by default to x86_64 machines. However, the default for Arm devices was a mere 240p. Marcan reckons what he observed is an outdated bias, given the plethora of multi-core Arm processors in modern devices.
One of the reasons for the bias might have been uncovered, though. "YouTube thinks aarch64 Firefox is... a HiSense TV?!" noted the developer — specifically a HiSense 65a67gevs. YouTube doesn’t allow the option of 4K playback on this TV for some reason.
With the YouTube / Firefox on Arm relationship analyzed, Marcan wondered what Google's own Chrome browser was doing when running on Arm hardware. He found a surprising little Google hack: "Chromium on aarch64 pretends to be x86_64." Thus, YouTube playback in Chrome using Asahi Linux defaults to 1080p playback and can be nudged to 4K.
After verifying his observations, Marcan decided to act on what he discovered. He filed a bug report with Mozilla, with the hope of getting Firefox updates to "report bull**** architectures." Marcan also decided to add some workaround code to Asahi Linux.
There's some follow-up discussion below the source report on Mastodon and the Hacker News site. Some early comments thought it was reasonable that YouTube defaulted to 240p on Firefox / Arm. However, it was pointed out that the change of UA also facilitated 4K playback, which was not an available option on Firefox + Linux + aarch64. Another interesting comment noted that Firefox, Chrome, and Safari on modern MacOS (running Apple Silicon) all have the UA set "incorrectly" to x86_64 by the developers. Thankfully, it's pretty easy to change your browser UA information, so you can set it to whatever you want to see what benefits may be available.
YouTube has had more than its fair share of headlines recently. It recently started aggressively checking for any kind of browser and extension-based ad-blocking. Not long after YouTube scripts were propagated to do this spying, a privacy consultant based in Ireland decided to file a criminal complaint. Also, last month Google was alleged to be crippling Firefox's performance by implementing video loading delays. YouTube released a statement in response to this accusation, but sadly the response seemed to be answering a question that hadn’t been asked — something about ad blockers. A UA switcher was again an easy solution to the issues observed.
