MX Player uses a powerful architecture that separates the user interface from the decoding engine. This allows it to leverage hardware decoding (using your device's GPU) for efficient, battery-friendly playback. However, hardware decoders vary across chipsets (Qualcomm, MediaTek, Exynos, etc.).
The VMD codec package serves two primary purposes:
Review Score: 2/5
This is where most users give up. You cannot simply install the app and hit play.
After installing the custom codec:
Because VMD files are distributed outside the Play Store, malicious actors have created fake "VMD codec" websites that host malware.
Red flags to watch for:
Golden Rule: Only download VMD from the link provided inside the MX Player app itself, or from the official XDA Developers thread maintained by the app's original creator (J2 Interactive).