Watching videos on Jolla's IPS screen is a real joy and although scaled to 960x540 resolution, HD videos still offer superior quality thanks to advanced encoding and higher bitrates. I've mostly played files from the SD card, because for example, the official YouTube app only supported HD over WLAN.

Now I've tried some other apps and I find Viral to be the best. It supports HD over 3G/4G, and continues to play in cover mode and with display off. It also has optional web login that works without Google Play services. In the app you'll see a three-dot icon in the top-right corner, from there you can access the settings, like default resolution (I set it to 720p). YouTube HD mod also works well but it doesn't find videos that aren't available on mobile.

On the browser front, Chromium-based Opera is able to play videos on both YouTube and Vimeo mobile sites, with playback controls ("HQ" = 360p/480p).

Audio is now in sync in all of these apps, great Maadajävri fix by sailors. If sound volume in Android is too low, you can boost it with Volume+ or some similar app.