Sony RDR-GX7 Technical Notes page 23

Comparison of constant bit rate (CBR) compression and variable bit rate (VBR) compression
Data volume
Variable
compression bit rate
Time axis
Constant
compression bit rate
Recordable DVD discs can be recorded not only using constant bit rate compression, but also
using variable bit rate compression, which enables high image quality recording of complex video
images at the same average rate as used in constant bit rate compression.
Bit rate
Impossible to compress all data
Average bit rate
Wasted bits
VBR compression using Sony's original algorithms
Clear
Bit
Even with the same VBR compression, if too many bits are used at the
beginning, the image becomes less clear toward the end of the recording.
The rate of compression is varied depending
upon data volume to enable all of the data to
be completely compressed without wasting bits,
thus increasing efficiency.
When the bit rate is fixed, signal coding is inefficient.
In portions where all of the data cannot be completely
compressed, playback quality deteriorates.
Fuzzy
Sony's original algorithms
maintain a consistently
high level of image quality.
Time
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