I had a need to merge 15 mp4 files recently and a simple tool for the job is Avidemux. Just open the first file and select Append from the File menu to select the next one. Repeat until all of your files have been added. The default encoding settings are copy for both video and audio so you shouldn't have to make any changes before saving the new file.
As with any encoding job it's always a good idea to test the output file. I have a new phone and for some reason the audio was getting messed up after the first clip. I've never experienced that problem in the past.
While researching the plug-ins piece of this series a problem with browser support became very obvious. My original intention was to test the websites with multiple browsers and report any differences, but quickly determined that my plan wasn't going to work. The sad fact was that Firefox (and presumeably Mozilla as well) was the only one to use the plug-ins properly.
There are many different video formats used by websites these days, and unfortunately, most of them are proprietary. After getting frustratrated by so many commercial sites ignoring Linux, I decided to do my own investigation of some noteworthy content sites to see if they are Linux friendly, can be made to work, or are downright exclusionary.
Where is the metadata standard for video? MP3's have ID3. Images have EXIF, IPTC, and more. If commercial video is ever to take off as an electronically distributed format it's necessary. Without it video players can't identify what's available. That may not seem important if you are sitting in front of a computer and reading a filename, but for other devices and 10' UI's it's a big problem.