On YouTube you can watch videos in 4K, without a 4K screen

On YouTube's Android app you can choose 4K resolution even if your smartphone has a lower resolution: bug or novelty?

The 4K resolution is quickly making its way to smart TVs and even streaming platforms, but on smartphones displays with this resolution are still a rarity. That doesn't mean you can't watch 4K videos on a smartphone with a lower resolution screen - they'll simply be scaled down with a loss in quality. Even 4K videos on YouTube behave like this, but now something seems to be changing.

In the latest version of YouTube app for Android, you can now set 4K resolution even if your smartphone doesn't support it. This was discovered by some Reddit users, who are also trying to figure out if it's a real new YouTube feature or a simple bug in the app, which no longer recognizes the real resolution of the smartphone display. There are good clues to believe both, and we'll only be able to know the truth for sure if this new feature is maintained in future versions of the YouTube app for Android. In the meantime, here's how 4K without a 4K screen works at the moment.

YouTube in 4K: is it a bug?

The theory that the ability to set 4K resolution even on non-4K screen is actually a bug is credible because this possibility is not present on all videos, nor on all smartphones with the latest update of the app.

We verified, for example, that YouTube's Android app allows you to set 4K manually on some videos, but only once: when you retry, the option disappears. In some cases, on the second attempt, the maximum available resolution becomes 480p. But even if you set it, the video is played at a resolution that is visibly higher than 480p.

This would suggest a bug in the app, which could be fixed in another update soon.

YouTube in 4K: is it a new feature?

On the contrary, to tip the scales towards the hypothesis that it's not a bug but a new feature there is the fact that playing the YouTube stream in 4K on a non-4K smartphone would still make sense, given the way YouTube works.

When a video is uploaded on Google's platform, in fact, its maximum resolution will be the original one of the video: a video uploaded in 1080p won't magically become 4K (i.e. 2160p). But the opposite is true: other versions of a video uploaded at 4K will automatically be created at lower resolutions. In questo modo il video sarà disponibile anche agli utenti con schermi meno evoluti, allargandone il pubblico potenziale.

Ma a cambiare tra una versione e l’altra dello stesso video non è solo la risoluzione: cambiano anche diverse impostazioni del codec video applicato per comprimere il video. Al momento i video di YouTube in 4K sono quelli con il codec settato per la qualità maggiore, quindi non è da escludere che YouTube mandi effettivamente allo smartphone un flusso video in 4K e poco compresso e che lo smartphone si limiti a fare il “downscaling" del video per riprodurlo sul display a risoluzione inferiore.