Keep screen at full brightness when playing a video

[mvglasow]

To reproduce:

Play a longer video (some 5–10 minutes, depending on device settings) and watch screen brightness.

Expected behavior:

Screen stays at the same brightness throughout the video.

Actual behavior:

After around a minute, screen brightness is reduced.

Versions:

1.2 (from F-Droid) on LineageOS 18.1

Additional information:

Screen brightness in Android is determined by at least three parameters:

• user-selected brightness level
• adaptive brightness dependent on ambient light (if supported by device)
• power management (which reduces screen brightness after a certain portion of the screen timeout has elapsed, which warns the user that the screen is about to be turned off)

I am referring to the third one. IIRC this can be inhibited through activity properties or by obtaining a wake lock when a video is playing.

Somewhat related to #93, which is about the screen turning off altogether

[mvglasow]

The dimming of the screen (as a warning of the impending turnoff) occurs a few seconds before the timeout. My system has a screen timeout of 2 minutes; the screen dims some 7 seconds before that. Since I have enabled a Developer Options setting to keep the screen on while charging, the screen doesn’t actually turn off while plugged in, but the “warning” dimming still happens.

Digging a bit deeper, there is PowerManager.SCREEN_BRIGHT_WAKE_LOCK to prevent that, although it is deprecated. The code to acquire the wake lock is:

pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
wl = pm.newWakeLock(PowerManager.SCREEN_BRIGHT_WAKE_LOCK, "WebTube");
wl.acquire();

The preferred method seems to be setting the android:keepScreenOn="true" property on an activity, which prevents the screen from turning off (including the dimming just before). I’d have to do some more research to find if this can be set dynamically, though.

[mvglasow]

Well, I found that one quickly. View.keepScreenOn(true) should do the trick, no permissions required. Source: https://stackoverflow.com/a/6553807/2703209