Welcome to the forum.
Am I correct that the MP4's contain the H.264 CODEC (that should be the case)?
What Project Preset are you using, determined at New Project?
How much free space do you have on your HDD's?
Conforming the Audio, and Indexing those files at Import, is important. For longer Duration files, and especially on a slower machine, it can take quite a few minutes. If one tries to edit, while the Conforming is on-going, it can cause hangs, crashes, or truncated audio. This ARTICLE goes into more detail.
Also, it might be good to list the specs. of your hardware now.
Hey Bill, thanks for the quick response.
It does use the H.264 CODEC. The project preset I'm using is NTSC-AVCHD-Full HD 1080i 30, although when I import the video to the project, I sometimes get a dialog box telling me that the project settings can be matched to the imported video, which I allow it to do. I have around 250GB of free space on my HDD. I allow the video and audio to conform and such on importing, I do not try to edit the video/audio while it is conforming. I'd also like to add that all files are transferred onto the HDD before the edit.
MacBook Pro 13" (Late 2011) running Mac OS 10.7.4 (Lion) I apologise, I had this wrong in the title and the original post.
Intel Core i5 2.4GHz Dual-Core
500GB SATA HDD
Intel HD3000 Integrated Graphics (if that's any help)
If there's anything else I need to provide, please let me know.
EDIT: I just tested editing a 10 minute video with the same file format and project preset, and, while it was hanging as frequently, it would only be for up to 5 seconds. Compared to the 50 minute video I was trying to edit, the hangs were much longer, sometimes becoming freezes. I know that if there aren't any immediate fixes and using the same video settings, I'll have to reduce the file size by reducing the length of the video, so cutting more frequently rather than recording long stretches.