In Recent versions of MX Player DTS & DOLBY audio codec supports are removed from the official MX-Player. If your video has dts/dtshd/ac3/eac3/mlp audio tracks it won’t play any audio. Only video will be played. Here’s a easy fix for that.
Here are the Steps
1. First you need to Know the correct codec required for you phone Go to Settings 》 Decoder 》Custom Codec. Codec required is usually mentioned there. If you are not sure then download the all in one pack (AIO)
2. Now you need to download the correct codec from below
For MX Player 1.7.32-40
For MX Player 1.8.0.Nightly (not compatible with 1.7.x)
Custom Codec v1.8.6 (For MX Player 1.8.6+)
3. After downloading the pack unzip it and again Go to Settings 》 Decoder 》Custom Codec and select the downloaded codec file.
Now MX Player will ask to restart do that and Done. To mqke sure the custom codec is properly installed, Once it restarts, from Options Goto Help 》 About. check whether the codec is loaded or not. If Custom Codec is loaded, it will show the platform & custom codec version below the MXPlayer version info.
Source : xda