Is there an option you can add to 'join' mp4 files together, or would this require another tool/command to offer this type of functionality?

I have tried using the join command via the Shell previously and it did 'join' the files together, but then playing the 'joined' files never played the additional mp4 files that had been added (joined) to the initial mp4 file.

It would be good to have such a feature / utility, but I haven't come across any utility that handles this option so that it plays the 'join'-ed files as yet.