Do not download from random pop-up sites. Look for the file named: mx_neon_1.49.0_repack.zip (Confirm the file size is roughly 5–7MB. If it’s 200KB, it’s fake.)
The term "repack" is unofficial. The official MX Player codec on the Google Play Store (titled "MX Player Custom Codec (AC3/DTS)") supports basic formats. However, the versions—often distributed on XDA Developers Forum or GitHub—include additional features: mx player custom codec 149 0 armv8 neon repack
The search for "MX Player custom codec 1.49.0 armv8 neon repack" The Ultimate Guide to MX Player Custom Codec