For the reproduction of video files in MB STUDIO the correct installation and configuration of the LAV video codecs is required
Download the codecs in the standard package from this page: https://codecguide.com/download_k-lite_codec_pack_basic.htm
After installing the codecs open the "Codec Tweak Tool"
Click on Win7DSFilterTweaker: Preferred decoders in the 32 bit column set all the options available on LAV Video
click on "Direct show Filters" click on LAV Video decoder and configure everything as in this image:
To speed up video mixes in MB STUDIO enable video prebuffer:
from Control Panel click on Power Options and set "High Performance"