I've been using QuickTime to trim MP4 files some over 1 GB in size.
Open the MP4 and select "Trim" under "Edit". What I like is you can click and hold down on the beginning or end markers and it expands the frames to allow for a finer selection. Then click "Trim" and select "Save" under "File". A new lossless MP4 is created minus the frames trimmed.
I use this feature to chop a large MP4 file into clips to reassemble later through QuickTime as well.
Note: My original files come from old DV tapes copied to my disk from an old camcorder as a folder of VOB files, (usually over 4GB per tape). These files in turn were converted to one large MP4 file with WinX DVD Converter for Mac ($). I've also tried MakeMKV (free) to convert the VOB files to an MKV file that could then be converted to an MP4. That last approach had issues.