Video file format wrappers are tricky because they can be generic in regards to the encodings inside of them.
In the case of a lot of AVCHD files, there are two encodings that might trip you up with playback in Photoshop: MPEG-2 video encoding and DOLBY audio encoding.
Both of these encodings are blocked in Photoshop unless 1.) You install PS as a CS6 Master Collection or CS6 Production Premium Suite product. or 2.) You install CS6 Premiere Pro or CS6 After Effects parallel to Photoshop on the same computer (note that AE also does not have a license for DOLBY audio content though, so that would still get blocked).
AVCHD files may-or-may-not have MPEG-2 encoding and may-or-may-not have DOLBY encoding. Some have both or neither. If either your audio or video aren't playing back then this is probably the case.
Note that you have to have a CS6 version of the suite or video apps installed for the content to be allowed with these encodings. There's also free software available to find the actual encodings inside of your video files. A software called HandBrake can give you an info dump of what encodings your files have.
I just brought a lot of .mts files in PS6 and it will play them but without the audio in the library tab. And this video format is not supported in the Develop Tab. This has to change. I have no use for this function if I have to convert my AVCHD files or follow all of the above you mentioned. I hope that in the final version this is addressed and it becomes as easy to import and edit as any other format. I find it dissappointing this is an issue at this point.
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