step 1. I have the most current version of quicktime 10.4
step 2 . when I got to os drive /library /quicktime there is no dvcprohdvideoOutput file in there. Also the not on that about the apple codec when I try to download and run it is says that it doesn't apply to me.
solutions regarding DVCPROHDVideoOutput QuickTime component from Apple
This problem occurs because QT32 Server, the process that After Effects uses to read and write QuickTime files, is crashing. One cause of QT32 Server crashing is a bad interaction with the QuickTime video out system when the Apple DVCPROHDVideoOutput QuickTime component is installed.
To work around this problem, do the following:
1. Go to [OS Drive]/Library/QuickTime.
2. Make a backup copy of DVCPROHDVideoOutput.component by dragging it to the desktop.
3. Now delete the DVCPROHDVideoOutput.component by dragging it from the Library/QuickTime folder to the Trash. Enter your password when prompted.
4. Empty the Trash. (This is an important step. Don’t skip it.)
Note: A couple of users have reported that, instead of the above instructions, installing the Apple ProApps QuickTime Codecs 1.0.2 update (http://support.apple.com/kb/DL1396) fixed the problem for them. You may try this solution first, though when we tested this it did not resolve the problem. We noted that the version numbers of the DVCPROHD component files were not incremented by this update.
I HAVE AFTER EFFECTS VERSION CC 220.127.116.11 2014
STEP 3. I can't find in preferences where to enable quicktime video preview in AE preferences. I did find Enable mercury transmit which is checked.
1. In After Effects CC (12.1), QuickTime video preview is disabled by default. You can choose to turn on the Enable QuickTime Video Preview preference to allow After Effects to preview video through external hardware on Mac OS X, at the risk of QT32 Server crashing. See this page for more information about After Effects CC (12.1).
2. In a release after that, we are planning to replace the legacy QuickTime video out system with a video preview system based on Mercury Transmit, related to that in Premiere Pro. We are also planning to extend the video preview system through Mercury Transmit to provide functionality beyond what is available through the current system.
step 4 I did not try since I am not having crashing issues.
Don't use QuickTime 10.x
Do use QuickTime 7.x