After I opened AVCHD with Quicktime, opened some videos, and then closed Quicktime, my AVCHD folder does't appear as a Quicktime icon anymore but as a folder... How do I get my AVCHD folder to reappear as a Quicktime icon?!
Not sure what you really want here. A "folder" is merely the graphic representation of a directory. As such, you can "associate" any custom icon you wish by simply dropping that icon to the top area of the "Info" window for that folder. However, this does not change the behavior of the folder—only the way it looks in the Finder.
...and the BDMV appears as Document.
Not an AVCHD camcorder user but I play around with a lot of BD content. Based on this experience and the article you referenced for this topic (HT202557), I suspect the same storage workflows may apply. Basically the document cited states "To access your clips in the media, open the folder and double-click the file named AVCHD, BDMV, or PRIVATE... If your AVCHD media has a single video clip, then QuickTime Player will simply open the clip in a player window." I suspect your AVCHD container may currently contain more than a single file. The implication of the above quote is that when the storage container holds more than one file, its behavior may change. Based on this, what happens when you treat the AVCHD media storage container as a "package document" rather than a "folder" or "media file?"
On my system, if I open the main media folder I see the following:
My BDMV container holds several folders and files and serves as a "package document" here. Double-clicking on its icon also returns a "Cannot Open" modal message. However, if I use the "Context" menu to "Show Package Contents," this is what I see:
At this point I suspect that different devices probably store their media files differently—either stored directly in the "package" file or stored in a sub-folder contained in the "package" file. In my case, the actual media stream (M2TS) files are stored in the "STREAM" folder as seen here:
As you can see in the above example, my "STREAM" folder contains 32 media files—the video of which can be viewed directly by QL and/or the QT X player app. Unfortunately, in my case, most of these files have DTS audio streams which are not natively supported by QL or QT X and for this reason, I normally play my content using the VLC player which has built-in DTS codec support. (Am assuming AVCHD camcorder files normally contain AC3 or LPCM audio and would, therefore, play both audio and video without problem for you.)
In any event, this brings us full circle back to the question, "What happens if you open the BDMV document as a 'package' file?" Do your clips then show up in the "package" container directly or in a folder within the "package" container? Once again, I believe the specific way the media files are actually stored will depend on the device and manufacturer. In any case, you can try this approach to see if it helps gain Finder-level access to the media files.
