First make sure you have FFmpeg installed. Follow this guide if you haven't already:
To remux a media file container with FFmpeg, simply copy all streams across to the new file using
-map 0 -c copy and then change the file container:
ffmpeg -i "C:\Transcode\input.mkv" -map 0 -c copy "C:\Transcode\output.mp4"
FFmpeg will give an error if it's not possible to remux the file into the specified container (different containers support different codecs and stream types).
You can automate this process on your files using the following Tdarr Plugin:
Get started using Tdarr transcode automation for free with this link: