Although some folks complain that Compressor is more trouble than it’s worth, I use it regularly to create self-contained QuickTime files and format conversions. No problems, really, until this evening.
Encoding a QT video from the Animation codec to a custom H.264 file resulted in Compressor generating “QuickTime error -120.” My was Mac was recently rebooted and neither Final Cut Pro or QuickTime Player was loaded at the time.
The problem was resolved using a suggestion from Apple’s discussion forum. In summary:
As a workaround for the -120 errors, I noticed the Compressor application menu has a choice for Reset Background Processing… which does get things working again, but isn’t really a good solution and suggests there’s a bug in the background application (qmasterd).
FWIW, the forum post is dated May 12, 2007 and I experienced this error on May 26, 2008 – one year and software version later.