Open Radar

 
Summary:
If Time Machine is enabled on a laptop running 10.7.2, it does an hourly "local backup". When this kicks off, it breaks QuickTime file writing. (In our app we can see that BeginMediaEdits returns -49 at the moment the local backup happens.)  

We see this on our app and the issue is also being reported by many iMovie '11 users on the Apple forum when trying to export movies.  Users are reporting that it fails randomly during long exports. (This is because it only fails if they happen to be exporting at the time the hourly backup happens.)

Steps to Reproduce:

To repro manually, or on a non-laptop, you can kick off the local backup manually by doing "sudo tmutil enablelocal" (disablelocal turns it back off). 

It's easy to reproduce in iMovie '11 9.0.2:

1) Turn on Time Machine on 10.7.2
2) Make an iMovie composition that is a few minutes long.
3) Choose to "Export using QuickTime". (I set it to export to DV.)
4) When it's about halfway finished exporting, run "sudo tmutil enablelocal"
5) It doesn't give an error immediately, but when the export finishes, you'll get a message:  "Unable to export movie. The movie could not be exported because an error occurred. (File already open with with write permission)"

Expected Results:
Time Machine should not cause quicktime exports to fail.

Actual Results:
Export fails as described above.

Regression:
Bug started in 10.7.2. Will only happen on laptops because that's when "local backup" are enabled.

Notes:
Here's the iMovie bug discussions:

https://discussions.apple.com/message/16676550#16676550
https://discussions.apple.com/thread/3460365?start=0&tstart=0
https://discussions.apple.com/message/16517882#16517882

Here's someone reporting what is probably the same bug in Telestream:

http://forum.telestream.net/forum/messageview.aspx?catid=42&threadid=9290