User manual

124 Appendix: MPEG Encoder Settings
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Resolution: Width and height of the video corresponds with the
settings in the export dialog.
GOP structure: Here you can change the settings of the GOP (view
page 130) sequence, i.e. the number of P frames per I frame within a
GOP. Please note that the total length of the GOP must not exceed
15 frames, which corresponds to the default setting (1 I frame + 4 P
frames + 5*2 B frames = 15 frames).
However, you can reduce the length of the GOP sequence (while
compromising the image quality at the same bit rate). This speeds up
the encoding process considerably as the motion estimation while
encoding P and B frames requires high CPU performance. The speed
of decoding, i.e. playback, is also increased.
If I frame is set to 1, each frame is an I frame. If the value is set larger,
the setting describes the total length of the GOP.
Auto GOP: Closed GOPs do not contain relations to frames from
subsequent GOPs. MPEGs where all GOPs are closed, make MPEG
editing easier as the I frames only can be edited alone if the GOP is
closed. Auto GOP closes GOPs at scene changes, whereby two
different and complex procedures ("fast" and "VSCD") are used.
Bit rate mode
In "constant bit rate" mode a bit rate that constantly remains the
same is used. This option should be used for Video CDs, as it is only
requried here. With a constant bit rate the full power of MPEG
compression can not be used properly as bandwidth for non-moving
scenes is lost.
"Variable bit rate" mode attempts to adjust the available storage
space to the requirements of the video you want to encode. The
actual bit rate fluctuates around a mean value. During calm sections
of the video it may drop to a minimum value, if there are movements
in the scene it may rise to the maximum value. There are two different
regulation processes (mode 1 and mode 128).
Advanced video settings
MPEG profile and level: The MPEG-2 standard defines so-called
"profiles" and "levels". For creating SVCDs and DVDs you can use
"Main profile and Main level". The high profile adds additional