AVCHD was created by Sony and Panasonic.
One of the problems of native AVCHD editing has nothing to do with the OS. It has to do with processing power. Most computers today, even with 3ghz dual cores, cannot do it properly. So it has to be converted to something that the computers can work with.
As I understand it AVCHD isnt designed to be played back raw, but decompressed.
If you want to play them in WMP, just download a powerful MTS Codec software like Aunsoft Final Mate.
Windows Media Player plays the "raw" files if you have something like CoreAVC installed.
VLC - VideoLAN Mac, Win Free Has interlacing problems. VLC has pretty much every codec built in so it can play any file format, but I find that the MTS files do not look that great (they seem washed out). If you have the correct H.264 codecs installed on your system, then Windows Media Player will in fact play them. Roxio Toast v11 Titanium Mac $80 WinX HD Video Converter does De-interlacing - $36 for Windows | for Mac Microsoft Windows Media Player mts player Win freeLinks:
MTS File Extension - Open .MTS files
Win X software for AVCHD(MTS) video Windows PC
Mac OS X.
How to Play AVCHD (.mts / .mt2s) on Mac OS X? - MacRumors Forums
What is the best player to play .mts files