Hi Tony! I notice you still haven't filled in your System button, so we have absolutely no idea what computer resources you have. However, AVCHD is the most demanding of all high definition formats and you need a fairly high powered computer to even play it back smoothly (Core 2 Duo or higher).
If editing it, and your computer is not particularly powerful, you should use the VS11.5+ SmartProxy feature, which essentially creates standard definition mirror images of your high def files. This can take time to do. But once done, you edit those proxy files in real time, and when editing is done, the changes are applied behind the scenes to the high def files. This will allow for successful edits, though I repeat you still need a powerful computer to play them back properly. My "old" P4 3.0 GHz with HT, NVidia 7600 GT graphics and 2 GB RAM, could edit AVCHD successfully (if slowly) but playback was jerky, so I initially though the edit had failed. But when I transferred the file to my Core 2 Duo 2.4 GHz laptop, it played back fine (and of course also does in Core 2 Quad).
SmartRendering is another useful feature ... when it works. (Maybe I am lucky, but it has always worked for me since VS7!
) Essentially, though it only works in rendering a project in one format to a new file in the same format. So in your case, it would be AVCHD after editing being rendered to a new AVCHD file. Essentially, SmartRendering means that only those parts of the video which have been edited will be rendered again. This not only speeds up the rendering time enormously, but with lossy formats like mpeg (and AVCHD is mpeg-4), it minimises loss of quality.
However, some people -- by no means a majority -- and particularly those with less well-resourced computers, had out-of-sync problems when using SmartRender. Turning it off seemed to resolve that problem. And if you start with high quality video (which AVCHD is, by definition), then rendering once and maintaining high quality settings will not normally result in any loss in quality that the naked eye can detect.
I should add that in the past, these out of sync problems related mainly to mpeg-2. I had not even thought about AVCHD using SmartRender, though now that I check a recent AVCHD project I did for another user here, my Core 2 Quad used SmartRender (or at least the box was ticked) with no problem.
