Well, it turns out the solution has been under my nose the whole time! My current editing software Ulead Video Studio Pro X2 *CAN* edit HD without too many problems at all on my current (not high end) hardware. I found an option in the program preferences called "Smart Proxy" which was caching(?) video if it was over 720x576 SD. All I did was disable this and HD editing directly on my 1280x720 MP4 files now works a treat! And this is still with all my other programs open in the background, I haven't optimised my system yet, nor put in more RAM.
Trimming is still not as smooth and instant as SD, but certainly quite usable now. Previews are seamless. I'm yet to give it a full run on a blog from start to finish, but loading and playing with an existing project it now looks good, a big improvement from before. As a bonus I also found that the output render option for HDV 720p (25fps) is about 10 times quicker than the previous manual 1280x720 MPEG2 option I was using. So my rendering is now lighting quick as well. I still have the hassle of having to convert the outputted 1280x720 MPEG2 into my final 1280x720 MP4, but there are plenty of solutions for that. MPEG StreamClip is faster than before with this different output encoding too, so that helps. But I'll look into faster programs to do this. So there you have it, YOU CAN edit MP4 files directly on ordinary hardware! I can film my blog in HD 1280x720 30fps MP4 on my Xacti HD1010 and copy the MP4 files directly to my drive and drop straight into the timeline in VS Pro X2 and trim and edit without any conversion or other messing around. Then just hit the output option which renders MPEG2 really quickly, and then I convert to MP4 using whatever standalone program. Dave.
