Have I to open the packet to see the .MTS to transcode them ? It's a bit freaky isn't ?
I normally just drop load MTS files to the VLC media player. If you really need the file to play in the QT X media player, try changing the file extension from ".MTS" to ".ts" and drop loading it to the the QT X player app. If you wish to retain the original "package" file in tact, dulicate the ".MTS" file first within the package and then drag the duplicated file to your desktop before changing the extension for playback in the QT X player.