It’s 19 (Android 4.4).
Yes. We fixed video views, and for that we needed a library which requires API 19. See Use new androidx.media2 video playback library by maniac103 · Pull Request #1503 · openhab/openhab-android · GitHub
Please also note we’ll bump the min API level to 21 (Android 5.0) soon … see [SOLVED] Raise minimum supported Android version to Android 5 for the rationale.