An upcoming version of the YouTube app for Android will let you set a preferred video quality for streaming. This feature was discovered in APK version 15.12.33 and given the all-caps "BETA" notes next to the new toggles, it seems that there might be a few bugs left to iron out.
Currently, YouTube has a default video quality that is set server-side. Speaking of, Google decided to reduce the global streaming quality, setting the default to 480p to free up bandwidth for other uses. Of course, while watching a video you can switch to HD quality manually, but the next video will start playing in 480p again.
Once this feature lands, you will have two separate controls for default video quality - one for when the phone is connected to Wi-Fi and one for when you're using your mobile data. There's a limited version of this right now, a toggle that defaults to 480p on mobile data and HD on Wi-Fi (well, it used to be HD, until yesterday's change).
Video quality preferences Adjusts to give you the best experience for your conditions Auto (recommended) Uses more data Higher picture quality Select your default streaming quality for all videos. You can change streaming quality in player options for single videos. Video quality preferences (BETA) Lower picture quality Data saver VIDEO QUALITY ON MOBILE NETWORKS VIDEO QUALITY ON WI-FI Video quality preferences (BETA)
This new feature will be useful after the COVID-19 outbreak is over, especially if you watch on a larger screen like a tablet. Actually, this feature may not become available until the outbreak is over if Google is serious about reducing the load on the Internet infrastructure.
YouTube can't hear you from here.
That's temporary. 640p will stop in a month, give or take. They did that to limit the bandwidth usage to counter the heavy load of users in home under quarantine.