how can I record a video on android AR app?

Option A : You find a app for andorid that can record the screen. Option B : Use a asset to integrate into your app to record it from inside your app This asset might be a option (https://assetstore.unity.com/packages/tools/integration/natcorder-video-recording-api-102645)

Option A : Already answered above

Option B: Only works with Android https://github.com/thanh-nguyen-kim/Unity_Android_Screen_Recorder You'll have to play with the resolutions in the Android script here to tweak the bitrate and the resolution of the output video. Works out of the box in portrait mode.