3
Table Of Contents
- Compressor 3 User Manual
- Contents
- Welcome to Compressor
- Getting Started Quickly
- Ways to Use Compressor
- The Basic Transcoding Workflow
- The Compressor Interface
- Setting Compressor Preferences
- Importing Source Media Files
- Creating, Previewing, and Modifying Settings
- Finalizing Jobs and Submitting Batches
- Creating AIFF Files
- Creating Dolby Digital Professional Output Files
- About the Dolby Digital Professional Encoder Pane
- General Information About Creating Dolby Digital Professional Files
- Converting Stereo Audio Files to Dolby Digital Professional Format
- Assigning Files to Surround Sound Channels (Manual Method)
- Assigning Files to Surround Sound Channels (Automatic Methods)
- Assigning Files to Surround Sound Channels with Droplets
- Options for Spatial Mixing
- Creating DV Stream Output Files
- Creating H.264 for Apple Devices Output Files
- Creating H.264 for DVD Studio Pro Output Files
- Creating H.264 for Blu-ray Disc
- Creating Image Sequence Files
- Creating MP3 Output Files
- Creating MPEG-1 Output Files
- Common Uses for MPEG-1
- MPEG-1 Specifications
- About the MPEG-1 Encoder Pane
- About the MPEG-1 Video Tab
- About the MPEG-1 Audio Tab
- About System and Elementary Streams
- MPEG-1 Transcoding Workflow
- Configuring the MPEG-1 File Format for Web Use
- Configuring the MPEG-1 File Format for DVD Use
- Creating the MPEG-1 Video for DVD Setting
- Creating the MPEG-1 Audio for DVD Setting
- Optional—Creating an MPEG-1 for DVD Group and Destination
- Creating MPEG-2 Output Files
- Creating MPEG-4 Output Files
- About MPEG-4 Part 2
- About the MPEG-4 Part 2 Encoder Pane
- Using Default MPEG-4 Part 2 Settings
- Customizing MPEG-4 Part 2 Settings
- Audio Podcasting Workflow
- Stage 1: Configuring the MPEG-4 Output for Audio-Only Output
- Stage 2: Including Podcasting Information
- Stage 3: Applying the Setting to a Source Media File’s Target
- Stage 4: Entering Annotations for the Output Media File
- Stage 5: Creating and Configuring Markers for the Output Media File
- Stage 6: Submitting the Job and Verifying the Output Media File
- Adding Additional Settings and Presets
- Creating QuickTime Movie Output Files
- Creating QuickTime Export Component Files
- Adding Filters to a Setting
- Working with Frame Controls
- Adding Geometry Settings
- Adding Actions
- Using the Preview Window
- Creating and Changing Destinations
- Using Droplets
- Appendix A: Keyboard Shortcuts
- Appendix B: Solving Problems
- Resources for Solving Problems
- Solutions to Common Problems
- Exporting from Final Cut Pro and Distributed Processing
- QuickTime Reference Movies
- Cluster Settings for Extended Transcoding Sessions
- Cleaning Up Cluster Storage
- Using Apple Qmaster with an NFS Server
- Apple Qmaster Distributed Processing and Xsan
- Compressor Command-Line Usage Requires Login
- Create Blu-ray Disc Job Action
- Contacting AppleCare Support
- Appendix C: Using the Command Line
- Installing Apple Qmaster from the Command Line
- Using the Command Line for Distributed Processing
- Using Scripts to Run Apple Qmaster, Compressor, and Batch Monitor
Open and Closed GOPs
Open GOPs are most efficient because they allow an extra B-frame in the GOP pattern.
Open GOPs start with a B-frame that is able to look at the last P-frame from the preceding
GOP as well as the first I-frame of its own GOP.
:06 :07 :08 :09
:09
:10 :11 :12 :13 :14 :15 :16 :17 :18 :19 :20 :21:04 :05
Open GOP
(IBBP, 15 frames)
I B B P B B P B B P B B P B B IB BP
:03
:06 :07 :08 :10 :11 :12 :13 :14 :15 :16 :17 :18:04 :05
Closed GOP
(IBBP, 15 frames)
P B B P B P B P B PI B BBB
By definition, closed GOPs cannot contain any frame that refers to a frame in the previous
or next GOP. In contrast, open GOPs begin with one or more B-frames that reference the
last P-frame of the previous GOP. Closed GOPs created by Compressor always begin with
an I-frame.
Open GOPs generally provide slightly better compression than do closed GOPs of the
same structure and size. The illustration above shows that a closed GOP contains one
more P-frame than does an open GOP of the same length. Since P-frames generally require
more bits than do B-frames, the open GOP achieves slightly better compression.
There are limitations to using open GOPs for DVD-Video discs that are created using a
DVD authoring application such as DVD Studio Pro. One limitation is that only closed
GOPs are permitted within MPEG-2 streams that will be used for mixed-angle or multi-angle
DVDs.
The other limitation is that DVD chapter markers can only be set at the beginning of a
closed GOP. The best time to define chapter markers is before doing MPEG-2 transcoding.
For example, if you specify your chapter markers in Final Cut Pro, you can set Compressor
to do MPEG-2 transcoding with open GOPs. Compressor will then force a closed GOP to
begin only at the specified chapter markers and will make all other GOPs open. You can
also accomplish this by specifying “forced I-frames” in the Compressor Preview window
and giving them a chapter name to be used by DVD Studio Pro.
However, if you want to specify chapter markers at any GOP boundary after your video
has been transcoded in the MPEG-2 format, you should use only closed GOPs. This freedom
is limited, as it allows you to set chapter markers only at GOP boundaries, rather than at
any video frame.
212 Chapter 18 Creating MPEG-2 Output Files