If you need to join together a number of MP4 files you can use the free and easy to use MP4Joiner utility by Alex Thuring.
The utility is free to download and use and can be found on the official MP4Joiner website http://www.mp4joiner.org/. The site provides binaries for Microsoft Windows and Mac OS X.
The source code is also available so you could compile for another platform if required.
Note: You can only join clips that share the same properties. They must be the same resolution, aspect ratio and frame rate. Ideally they should have been encoded using the same settings. When I've used this tool I have usually been joining together clips I have exported from my video editing application using the same encoding preset.
Step 1 - Download and Install
Download the binary for your operating system and run the installation.
During the installation you will need to accept the terms and conditions. It also offers to install some additional software. Carefully read each of the screens you are presented with and use "Skip" and "Decline" if those other utilities don't appeal to you.
Step 2 - Run and Load Files
Run MP4Joiner and you will be presented with the following screen:
Either drag and drop your MP4 files into this window or use the "Add Video" button. You will see a preview of your files as shown in the example below :
Some of the video properties are summarised next to each clip.
Step 3 - Generate Output File
To start the joining process make sure you have one of the video files selected as this will enable the "Join" button.
Click the "Join" button.
You can either accept the default "Output.mp4" filename or type a different one.
When the output file has been created you will see a screen like the example below:
The time it takes to complete will vary depending on the speed of your PC. It might be worth testing on a few clips before you attempt to join lots of files together.
For reference here is the information that is displayed when the "About" button is clicked :
This tutorial is also available as a "How To" video on YouTube :