Here comes a fast way to change video formats with TDMore Video Converter.
If you have MKV files, just add it to TDMore Video Converter and select MP4.passthrough to change the video format in seconds.
You can do it to. Learn more about TDMore Video Converter at:
I tested a sample MKV video with size of 199MB 52 seconds,
Attached below is the screen shot and media info for the output sample video.