QuickTime Player in OS X Mountain Lion or later allows you to play, inspect, trim, export, and share video from AVCHD media. The AVCHD format is used by high-definition consumer devices such as hard-disk–based camcorders and digital still cameras with video.
AVCHD media is usually accessed by connecting your camcorder or camera to your Mac via a USB cable. Some devices, such as digital cameras, have removable memory cards that can be read using a USB card reader or the SD card slot included with some Macs. Check the documentation that came with your device for information about how to transfer AVCHD media to your Mac.
After transferring the AVCHD media to your Mac, open the folder that contains the media. Then double-click the file named AVCHD, BDMV, or PRIVATE to open it in QuickTime Player.
If the media contains multiple clips, you might see them grouped together, sorted from oldest to newest. Select one or more clips that you want to play, then click Open: