the open source media converter is nice! thanks!
i had the same problem with my new sony rx100 (avc/ac3 1080p 50p), when i was not able to playback the 50p clips on my macbook pro 2010. except with vlc, but with shutter and high cpu load.
Alans script worked nice to rewrap .mts to .mp4, but still the i had a high cpu load, and the clip was shuttering in qt player, and there were audio problems (only one channel,etc...).
after some reseach i found out that the ac3 stram is decoded via perian, because when you unistall perian in system preferences there is no sound at all in qt x.
(for those who wonder - vlc uses its own decoder)
thanks to the tip from "veg" to the "open-source app called Media Converter"
http://media-converter.sourceforge.net/
and the script "rewrap-avchd-mov-pcm.mcpreset" everything is smooth as butter!
the audio is converted to pcm, and the avc/h264 stream is rewraped to a .mov file (is now the sort of same container like a canon 5D2 h264/pcm .mov file). which is still very fast, because only the audio is converted to "uncompressed".
cpu usage is about low as 10%, smooth 50p playback and sound ok!
perfect playback solution, but still not editing friendly on my macbook pro (too high cpu load in FCPX)