your computer is much to slow to playback the video correctly
I'm a newbie to AVCHD, just bought a Canon HG20. I shot some video which I've downloaded a few times using various software, and depending on which software I use for playback, it has a problem on every one. Usually it's the video running in "slow motion", or should I say a "strobe effect", like it's missing every other frame, and the audio has an intermittent echo to it, like a DJ "scratching" repeats. Sometimes the video is still and the audio is running fine, and sometimes the video is OK but no audio. I've tried downloading with 4 different programs and it's the same problem.
Since I'm having problems with numerous download and playback programs, and since the source video/audio is OK when I play it back on my camera, I assume my problem is in my PC's drivers. I'm converting the raw .m2ts file to an .mpg file and I have no problem playing those on my PC otherwise.
I have a P4 2.4GHz CPU & 1GB RAM and I'm running Win XP Home. It's a older system, but it serves me well otherwise.