If you’re using OS X and you copy AVCHD media folders to a NAS (network-attached storage) or a case-sensitive disk, you may run into problems: opening the media in 10.8’s Finder gives you “CANNOT OPEN” instead of a clip browser, FCP X can’t see the clips, and so on.

Cannot Open? Must be OS X failing to figure out an AVCHD folder…

OS X’s AVCHD handling is very brittle. It follows a strict definition of the AVCHD folder and file definition, any deviation from which breaks OS X’s interpretation. For example, deleting the playlist file (typically 00000.MPL, at least when my Panasonics record it) means that OS X won’t see any clips, even if the underlying .MTS files are all present and intact. Deleting one of the .CPI files causes OS X to present its clip as an undefined square, and trying to play it gives an “Undefined error”. Yet the underlying video is still present; VLC can still play the corresponding .MTS files.

OS X is stricter about the AVCHD spec than many cameras: the spec uses 8.3 filenames, and such filenames are expected to be uppercase. Yet not all camera write uppercase filenames; I have Sony-generated media in “private” folders instead of “PRIVATE” folders, while some Panasonics will save the index file as “index.bdm” when individual clips are deleted in-camera, instead of “INDEX.BDM”.

When a mixed-case folder structure is accessed on its original SD card, or transferred to a Mac’s default filesystem (HFS+, case-insensitive), no problems occur: a search for “INDEX.BDM” returns that file regardless of case, and OS X can see the clips. But if you store that folder structure on a NAS box running Linux (which many of them do, including NASes from Netgear, Synology, and QNAP), or on a case-sensitive HFS+ disk, your media may no longer be understood by OS X or Final Cut.

The fix is simple in theory, annoying in practice: simply walk the folder structure and change any mixed-case or lowercase file and folder names to uppercase. Doing so lets OS X and Final Cut see the clips, and even iMovie will “Import Camera Archive” when pointed at the enclosing folder.

The annoying bit is that, if “index.bdm” is buried three levels deep in uppercase folders, OS X still presents those folders as “AVCHD Content” objects; you have to use “Show Package Contents” multiple times to get to the offending file.

I got tired of doing this manually (I shoot with a Panasonic GH2 and a GH3, so I have to do this a lot), so I wrote a little utility to do it for me:

avchd2AVCHD automates the finding and fixing of lowercase AVCHD filenames.

If you’d like it, here it is. No charge, but you get what you pay for, grin. It’s been tested to work on my Mac and my Netgear NAS, but that’s it: you are a beta tester if you decide to use it! Make sure you try it out with expendable media before you unleash it on your precious, irreplaceable footage (and it’s best to have backups of that footage, just in case).

Disclosure: There's no material connection between me and Sony, Panasonic, or Apple. No one offered me any compensation for this writeup.