I did format the card after turning it back into a "camera" card, but the problem is that I asked the camera to do the formatting, and it did a half-assed job. (The AppleTV patchstick writes out an HFS+ image, I believe.)

PhotoRec has now been running for 1.5 hours. It estimates it will take it another 17 hours. It's gotten maybe 6% through "phase 1" and has recovered nothing so far. Not promising.

If I give up on PhotoRec, I'm liking the idea of just dd'ing an image of the entire SD card. Or, maybe TestDisk can somehow patch things together again. Hrm.