Apple Compressor (4.0) - Manual (Page 107)

Chapter 5 Custom settings and output formats 107
About system and elementary streams
You can use Compressor to create system or elementary MPEG-1 streams.
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System streams: System streams, also known as multiplexed streams, combine the video
and audio components into the same file. This type of stream is most often used in
web applications.
Compressor automatically creates a system stream when you enable both the Video and
Audio tabs in the same setting.
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Elementary streams: With elementary streams, there are separate files for the video and audio
components. Elementary streams are required by some applications.
Compressor automatically creates an elementary stream when only the Video or Audio tab
is enabled, but not both. To create elementary streams of both the video and the audio, you
must use two settings—one with the Video tab enabled using the file extension .m1v and a
second with the Audio tab enabled using the file extension .m1a.
MPEG-1 specifications
Compressor supports all the MPEG-1 specifications for frame sizes, frame rates, video encoding,
and audio encoding.
MPEG-1 frame sizes and frame rates
Compressor can produce full-frame-rate video (25 fps and 29.97 fps for DVD and 23.976 fps, 25
fps, and 29.97 fps for the web) with SIF resolutions dependent on the use.
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Web: 320 x 240
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NTSC: 352 x 240
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PAL: 352 x 288
Although the NTSC and PAL resolutions are roughly half the full resolution of MPEG-2 video,
when played on a DVD player they automatically expand to fill the entire screen.
MPEG-1 file format specifications
MPEG-1 video encoding uses a process very similar to that used in MPEG-2 encoding—many of
the same terms and settings apply. In Compressor, the encoding settings are set as follows:
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Encoding mode: One pass
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GOP structure: Open
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GOP pattern: BBIBBP
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GOP length: 15 frames for NTSC; 12 frames for PAL
These settings are fixed and apply to all Compressor MPEG-1 video output files. For information
about group of pictures (GOP) settings, see
MPEG-1 Encoder pane on page 112. For information
on the encoding mode, see MPEG-1 Encoder pane on page 112.
You can force the creation of I-frames at specific points in the MPEG-1 output files by placing
compression markers on these frames. You can add these markers to the source media file using
Final Cut Pro, or you can add them manually in the Preview window. For more information, see
Markers and poster frames overview on page 46.
The MPEG-1 format does not support named chapter markers.