Because Google no longer serves legacy apps, you must side-load using an APK (Android Package Kit). Avoid random "free APK download" sites that bundle malware.
For a step-by-step walkthrough on installing and setting up the app: mx player for android 4.1.2
: A useful plugin that locks the screen during playback so children cannot accidentally place calls or open other apps. Installation Guide Because Google no longer serves legacy apps, you
On modern Android, MX Player uses HW+ by default. On Android 4.1.2, this feature is critical: this feature is critical: