Okay, I have successfully written an AppleScript that does what I want, however, now I have a new problem as there appears to be a bug in Mountain Lion that is preventing me from making this the default behaviour for ALL 'PRIVATE' directories. I can associate it with one directory but each new card I bring in, the PRIVATE folder isn't associated with the script.
I've tried looking through the actual com files to see if I can change the behaviour, but I am not finding anything.
Here is the Applescript that you associate with the PRIVATE previous directory. For the FS100 file structure, this opens up to the directory containing the MTS files.
Hopefully someone else can help us with the association part that is broken.
(1) Open up the app 'AppleScript Editor' that is installed with OSX.
(2) Paste in this script:
on open of finderObjects
repeat with i in (finderObjects)
tell application "Finder"
open folder ((i as text) & "AVCHD:BDMV:STREAM")
end tell
end repeat
end open
(3) Click the 'Compile' button to make sure everything is okay. This script works on the top-level file that used to be a directory. So in my case, I will be double clicking on 'PRIVATE' which if I show contents, contains AVCHD at the next level. Knowing this, you can descend down into the directory you want and replace "AVCHD:BDMV:STREAM" with what you need for your camera card structure.
(4) When you save or export the script, make sure you save it as type 'Application'. I call my script "Open AVCHD Folder" and I placed it in the Utilities under Application so I would not forget where it was. If you do place it here you will need to 'Authenticate' probably.
(5) Go to the file that used to be a directory in earlier versions of OSX (In my case 'PRIVATE') and right click and select 'Get Info'. Find the section for 'Open With:' and select the drop down menu and choose 'Other...'. At the bottom, Set 'Enable:' to 'All Applications' then go to the AppleScript binary that you created. Also, make sure you select the 'Always Open With' checkbutton at the bottom. You will see a message that it is not sure if it can open this sort of file, but it can (if you coded it correctly with any changes you made). Select Add.
(6) I tried to use the 'Change All...' button below 'Open with:' but it returned an error. As far as I am concerned, this is a bug with OSX. This will prevent you from getting this as a default behavior for all PRIVATE directories.
Until we can work around the Chnage All bug, this is still more steps and not a full solution.