A recent version of ffmpeg is required for AVCHD. It is run in the terminal and transcodes H264 to a mpeg2 transport stream which can be opened in Streamclip. I neglected to notice the original post was converting 25fps AVCHD video. In this case the framerate should be -r 25.
Originally Posted by Janke
Transcode directly to Quicktime with a command such as
Note that you can choose any audio and video codecs supported by Quicktime.
ffmpeg -i 00045.mts -r 25 -acodec pcm_s16le -vcodec mjpeg \
-flags +ildct -b 148Mb -f mov -y 00045.mov