Convert with FFmpeg

Always download open source software when possible. Don't be phished!

FFmpeg is a free and open tool used on virtually all platforms and is often used as the basis of that "free" program you downloaded to convert your videos

Don't download some sketchy program to convert your video, use FFmpeg instead

Using Windows Command Prompt

After getting FFmpeg, you can control it with cmd.exe

Copy and paste this into command prompt to remux all MKV files in a folder into MP4 files. If the video codec used in the MKV is compatible with MP4, it will be super fast.

You can use the AAC option instead of passing AC-3

Command prompt remux with ffmpeg
Force AAC
Command prompt remux with ffmpeg
for %i in (*.mkv) do ffmpeg -i "%i" -c:v copy -c:a copy "%~ni.mp4"
Force AAC
for %i in (*.mkv) do ffmpeg -i "%i" -c:v copy -c:a aac "%~ni.mp4"

Using Bash shell (Mac and everything else)

Here's the equivalent shell commands

Shell command Remux with ffmpeg
Force AAC
Shell command Remux with ffmpeg
for i in *.mkv; do ffmpeg -i "$i" -c:v copy -c:a copy -map_metadata -1 "$i".mp4; done
Force AAC
for i in *.mkv; do ffmpeg -i "$i" -c:v copy -c:a aac -map_metadata -1 "$i".mp4; done