For best performance with the new codec:

The is a specialized update designed to restore support for audio formats—specifically EAC3, AC3, and DTS —that were removed from the official app due to licensing issues . Performance Review

The "Repack" in the context of the MX Player Custom Codec 149.0 ARMv8 Neon Repack implies that this custom codec package has been specifically repackaged or optimized for use with MX Player on ARMv8-based devices that support Neon instructions. This optimization ensures that the codec can leverage the enhanced processing capabilities provided by Neon, potentially leading to smoother video playback and improved performance.