This page demonstrates the new HTML5 video element, its media API, and the media events. Play, pause, and seek in the entire video, change the volume, mute, change the playback rate (including going into negative values). See the effect on the video and on the underlying events and properties.
In AVIDemux select video=copy, audio=copy, format=mp4 – or format= (choose the format of your input files)
Click on File>Open and select 1.mp4 then click on File>Append and select 2.mp4, and add any additional files to append using the same method, File->Append
Click on File>Save>Save Video to save your output file and give it a name and extension of mp4 such as [final_file.mp4]
How to convert .flac files and other formats to .mp3 on OSX
Using this free application All2MP3