This is the simplest thing you can do to troubleshoot Compressor issues. Restarting your computer resets Compressor related system resources.

In order to verify that Compressor 4 is working as expected, it's always a good idea to review the documentation to ensure that you clearly understand the expected behavior of what you're trying to do. Following this step thoroughly could save a lot of time.

For information on how to access the Compressor 4 User Guide, see Final Cut Pro X, Motion 5, Compressor 4: User guides

See Compressor 4 - Technical Specifications.

Ensure that your computer meets the OpenCL-capable graphics card or Intel HD Graphics 3000 or later system requirement. For more information, see Final Cut Pro X, Motion 5, Compressor 4: Graphics card compatibility

Note: If you are actively working on a transcoding project, avoid updating or upgrading Compressor 4 until you are finished with the project. Either complete the project in the version of Compressor 4 you are currently working in, or ensure that you have a current backup of your Compressor custom Settings and Layouts and a backup of Compressor 4. This is so you can revert to the previous state that your Settings, Layouts, and the application were in if updating or upgrading to the latest version of Compressor 4 does not address your issue. 

For more information see:

• Mac App Store: Update applications
• Final Cut Pro X, Motion 5, Compressor 4: Issues updating on the Mac App Store

For more information see Final Cut Pro X, Motion 5, Compressor 4: Run Software Update after installation to install Pro Apps QuickTime codecs.

For more information see Compressor 4: Importing overview.

If you use any third-party software (plug-ins, tools, or content) with Compressor 4, contact the developer to ensure that the version of third-party software you have installed is compatible with the version of Compressor 4 you're using.

For more information see Isolating an issue by using another user account.

Removing the Apple Qmaster folder will allow it to be recreated the next time Compressor is launched.

1. If Compressor 4 is running, quit Compressor by choosing Compressor > Quit Compressor.
2. In the Finder, hold down the Option key and choose Library from the Go menu.
3. In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster folder to the Trash.
   
4. Restart your computer.

Important note before you begin:
Before resetting user preferences, be sure to first review your Compressor 4 preferences as they are currently configured, and note any specific settings you've chosen. When resetting the Compressor 4 preferences, your preferences will be returned to default settings the next time you open Compressor 4.

Also, verify that you have a current backup of your Compressor custom Settings and Layouts. These items are located in ~/Library/Application Support/Compressor. Custom Settings are located in the Settings folder and custom Layouts are in the Layouts folder.

These articles are helpful for understanding the different preferences:

• Compressor 4: Set Compressor preferences
• Compressor 4: Preferences window

  How to reset the Compressor 4 Preferences:
  Follow the steps below for the version of Mac OS X that you are using.

OS X v10.8 Mountain Lion

1. Create a new folder on the Desktop. Name the folder with a descriptive name you'll remember. For example, something like "Compressor 4 Preferences."
2. In Finder, hold down the Option key and choose Library from the Go menu.
3. In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster and Compressor folders to the folder created in step 1.
4. Return to the Library folder and open the Preferences folder. Move the following files to the folder created in step 1:

com.apple.Compressor.plist
com.apple.Compressor.plist.lockfile

com.apple.Compressor.LSSharedFileList.plist
com.apple.Compressor.LSSharedFileList.plist.lockfile

Note: The .lockfile item may not be present on your system.

OS X v10.7 Lion

1. Create a new folder on the Desktop. Name the folder with a descriptive name you'll remember. For example, something like "Compressor 4 Preferences."
2. In Finder, hold down the Option key and choose Library from the Go menu.
3. In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster and Compressor folders to the folder created in step 1.
4. Return to the Library folder and open the Preferences folder. Move the following files to the folder created in step 1:

com.apple.Compressor.plist
com.apple.Compressor.plist.lockfile

com.apple.Compressor.LSSharedFileList.plist
com.apple.Compressor.LSSharedFileList.plist.lockfile


Note: The .lockfile item may not be present on your system.

Mac OS X v10.6 Snow Leopard

1. Create a new folder on the Desktop. Name the folder with a descriptive name you'll remember. For example, something like "Compressor 4 Preferences."
2. In the Finder, choose Home from the Go menu.
3. In the Home folder that opens, open the Library folder. Then, In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster and Compressor folders to the folder created in step 1.
4. Return to the Library folder and open the Preferences folder. Move the following files to the folder created in step 1.

com.apple.Compressor.plist
com.apple.Compressor.LSSharedFileList.plist

After resetting preferences by moving the above file(s), perform the same steps that caused the issue to occur originally. If the issue no longer occurs, move the folder you created on the Desktop in the steps above, to the Trash. Empty the Trash to delete them from your computer.

Important note before you begin:
Before reinstalling, be sure to first review your Compressor 4 preferences as they are currently configured, and note any specific settings you've chosen. When resetting the Compressor 4 preferences, your preferences will be returned to default settings the next time you open Compressor 4.

Also, verify that you have a current backup of your Compressor custom Settings and Layouts. These items are located in ~/Library/Application Support/Compressor. Custom Settings are located in the Settings folder and custom Layouts are in the Layouts folder.

Removing Compressor 4
Follow the steps below for the version of Mac OS X that you are using.

OS X v10.8 Mountain Lion

1. In Finder, choose Applications from the Go menu.
2. Locate the Compressor application and drag it to the Trash.
3. In Finder, hold down the Option key and choose Library from the Go menu.
4. In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster and Compressor folders to the Trash.
5. Return to the Library folder and open the Preferences folder. Move the following files to the Trash:

com.apple.Compressor.plist
com.apple.Compressor.plist.lockfile

Note: The .lockfile item may not be present on your system.

OS X v10.7 Lion

1. In Finder, choose Applications from the Go menu.
2. Locate the Compressor application and drag it to the Trash.
3. In Finder, hold down the Option key and choose Library from the Go menu.
4. In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster and Compressor folders to the Trash.
5. Return to the Library folder and open the Preferences folder. Move the following files to the Trash:

   com.apple.Compressorapp.plist
   com.apple.Compressorapp.plist.lockfile

   Note: The .lockfile item may not be present on your system.

Mac OS X v10.6 Snow Leopard

1. In Finder, choose Applications from the Go menu.
2. Locate the Compressor application and drag it to the Trash.
3. In Finder, choose Home from the Go menu.
4. In the Home folder that opens, In the Library folder that opens, open the Application Support folder. Move the Apple Qmaster and Compressor folders to the Trash.
5. Return to the Library folder and open the Preferences folder. Move the following file to the Trash:

   com.apple.Compressorapp.plist

Reinstalling Compressor 4

• From the Mac App Store
  1. Follow the steps from earlier in this article to remove Compressor 4.
  2. Open the Mac App Store.
  3. Click the Purchases button in the Mac App Store toolbar.
  4. Sign in to the Mac App Store using the Apple ID you first used to purchase Compressor 4.
  5. Look for Compressor in the list of purchased applications in the App Store. If you don't see Compressor in the list, make sure that it's not hidden. See Mac App Store: Hiding and unhiding purchases for more information.
  6. Click Install to download and install Compressor 4.
• From a backup
  If you are reinstalling (restoring) a copy of Compressor 4 from a backup, you have two options. Choose one of the following:
  1. Simply drag the application back from its storage location to your Applications folder.
     Or
  2. If you use Time Machine to back up your computer, follow the steps for restoring data from Time Machine backups.

When you open the restored application for the first time, you may be required to sign in with the Apple ID account that you used to purchase the application.