This app continuously captures camera images in the background for timelapse videos (see video link for a sample).

Delay between images is adjustable down to 1 second.
Normal phone operation can continue with minimal CPU load.

Note: images are saved on SD card as JPEG. Not yet tested on Android 10 which introduced changes to external storage handling.

This app is open-source under GPL. The source code is available at https://github.com/floe/Background-Timelapse