I've been splitting MP4 (AVC H.264) videos of car races for years, and I've been using SMM for the last two using Version 7.x. Everything worked fine. I upgraded to version 8 (8.0.2211.15, then 8.0.2302.07) and it simply fails. Here's the issue.
I add a video (with 2 audio tracks). I begin setting markers. After about 3 or 4, the next time I try to set one, the preview screen freezes, the cursor advances quite a bit (sometimes to the end of the video). If I press Play, either the preview shifts to the new cursor location, or the preview screen goes black and the audio track continues from some location I cannot determine. Sometimes when I click Play the app just crashes.
I've tried 2 different videos, then I went back and tried videos that I had successfully split with version 7.6.2201.27. It failed in the same way on all files.
I completely uninstalled SMM and reinstalled with no improvement. I uninstalled and reinstalled version 7.6 and it works fine.
I'm happy with version 7.6, but at some point I'll need to upgrade, but until this issue is resolved I'll stick with 7.6.