You can download the codecs:
here ( Google Drive :: All versions )
here ( GitHub releases )
Also the XDA download tab is no longer updated as for some reason I cant remove them.
1. Check which version you need by going to Local Player Settings/Decoder/General
in the Custom Codec tab it will tell you which one is needed (x86,x86_64,neon,neon64/ARMv8).
Note: skip step 1 if your using aio (all in one) version
2. Download the one you need (No need to unzip it)
3. Go back to Local Player Settings/Decoder/General
and tap the Custom Codec tab then select the version you downloaded. DONE!
MX Player Custom Codec, Tool/Utility for the MX Player
Current Stable Version: 1.25.0
Last Updated 2020-06-25