[Alan Norman] “What is the most efficient way to work with the files to transcode please ?”
The best thing you can do, on a Mac at least, is to get EditReady and have it re-wrap AVCHD into single QuickTime (MOV) files. This is really fast because it’s not transcoding, it’s simply re-wrapping. This takes the AVCHD content out of the directory setups and gives you a simple *single* file to work with. And if clips are spanned over multiple MTS files, it will combine those as well.
On a Mac, if you do any amount of significant work with AVCHD, EditReady is a must-have.
Otherwise, if you have FCPX, you can also import AVCHD into it and it will do the same thing, then you can pull the resulting QuickTimes out of the library bundle. However, FCPX will rename them all, EditReady keeps the original naming convention (not that it’s much better, 00001.MOV for example).