The codec file you're looking for is likely a set of additional codecs for MX Player, a popular media player app for Android devices. The specific file you're referring to seems to be designed for devices with ARMv8 architecture and Neon support.
This guide covers the download and installation of the specific for MX Player version 1.49.0. This is commonly sought after by users who need support for older audio formats (like AC3 and DTS) which were removed from the official Play Store versions of the app due to licensing issues. The codec file you're looking for is likely