Software for splitting or trimming MP4 video without transcoding
Avidemux is a lightweight editor that can split videos without transcoding: 


Start Avidemux
Open a file e.g. by dropping it into the Avidemux window 
Choose where your video should start and then click on the (red) “A” button below.
Choose where your video should stop and then click on the “B” button below.
Select an output format (e.g. mp4). Note: there are two mp4 versions. If one does not work, just try the other.
Click on the save icon. Avidemux will propose a new file name based on the old one adding an “_edit” before the suffix. The trimming takes less than a second.