I needed to pull a bunch of video projects from my DVD archives this weekend. These are regular old DV-NTSC Quicktime movies, made from Final Cut Pro. But attempting to copy them from the Finder in Mac OSX 10.4.2, I noticed the estimated copy time seemed inordinately long: 45 minutes for 3.5 GB? I can burn a disc faster than that. Then, about halfway through, the copy operation choked, and I got an error message that said that the copy operation couldn't finish because some of the data couldn't be read.
Then I started scrolling through the files on the DVD, and as I touched them the files started disappearing before my eyes! Folder names also disappeared, but the folders were still there, but no longer navigable. Doing an ls in the Terminal showed everything intact. Copying the files using cp or ditto yielded complete and usable files.
After grabbing my data using the Terminal -- which not only worked, but worked quickly -- I decided to relaunch the Finder, and try copying one of the problematic folders. The folder appeared to copy, but the contents of the folder were incomplete. Only two of the thirteen original movies made it over in the copy. But this time, I received no error message. Then I tried copying individual files from the problem folder on the DVD. Some appeared to copy super-fast, and then just disappeared, while some copied fine, and at apparently normal speed. But the time estimation for some took a while, and for others, barber-poled indefinitely. In fact, the only way to stop the Indefinite-Barber-Pole-of-Death was to relaunch the Finder.
More tests: I tried another DVD. Copying that data worked perfectly: fast and error-free. I also put the problem DVD in my PowerBook running Panther and tried copying the data. And guess what? Same problem. Better error message though. And no disappearing files and folders.
So clearly, something is wrong with my DVD. But it seems really strange to me that, while a simple issue of cp or ditto works fine, if the Finder encounters the slightest disc error, it just gives up. This raises some questions: If the command-line can handle it, and the Finder can't, what is the Finder doing wrong? Moreover, why doesn't the Finder use cp or ditto? Or something that can handle these sorts of errors? Or, at the very least, why doesn't the error message offer some sort of useful information about what went wrong and how, via Terminal, one might go about extracting the data?
Finally, and I took a look at the DVD surface itself, and I have no idea how this happened, but it was scratched to shit. Looked like a Blockbuster rental. Awful. Anyway, the moral of the story? I don't know, actually. I guess one moral would be, "Take good care of your optical media; it is by no means indestructible." Moral two? If the Finder can't copy it, the command-line, perhaps, can.