Trim commercials from mp4 files without re-encoding
I used Elgato Video Capture hardware/software to transfer a VHS (TV movie recording) to my Mac. It created a file 1.45 GB that included commercials. According to Elgato's documentation (I know it's old) I can trim commercials in iMovie without having to re-encode it. I was easily able to trim out the commercials but was then forced to "export" the file (which seemed to re-encode) and resulted in an 8 GB file--more than 4 times the original file size.
I've read documentation that iMovie (current version 10.3.3) HAS to encode, so the Elgato documentation must have been for a MUCH older version of iMovie that dealt with files in a different way. I've also read that I can use Quicktime 7 to trim and save without re-encoding, but it doesn't seem that QT7 is compatible with Big Sur so I'm not even sure it's worth trying to find and download.
Does anyone know another way of trimming out the commercials without resulting in a file that is 4 times larger than the original?
MacBook Pro 13″, macOS 11.6