INS_CNVETX1_REV– 06/10/13 PAGE 58
INSTALLATION AND OPERATION MANUAL
CNVETX1
TECH SUPPORT: 1.888.678.9427
The advantages of VBR are that it produces a better quality-to-space ratio compared to a CBR file
of the same size. The disadvantages are that it may take more time to encode, as the process is
more complex, and that some hardware might not be compatible with VBR files.
In Constant Q mode only Q Initial is entered. This mode is intended to keep a constant quality.
A low Q setting will generally have a high bit rate providing high quality. A high Q setting will
generally have a low bit rate with lower quality.
Each mode has its own relevant parameters. Other parameters are shaded.
Bit rate
The Bit rate parameter is the bit rate of the stream. The Bit rate can be set to a value in the range
of 50000 to 10000000.
The rate control mode determines the required parameters.
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Average Bit rate: Average bit rate of the video stream (VBR mode only).
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Maximum Bit rate: Maximum bit rate of the video stream (VBR mode only).
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Constant Bit rate: The bit rate of the video stream (CBR mode only).
Quantization
The Q (Quantization) parameters are quality settings, where 20 is lowest quantization and highest
quality (and more bits used), and 51 is highest quantization and lowest quality (and less bits used).
The rate control mode determines the required parameter.
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QMin: Minimum quantization that is used for encoding.
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QMax: Maximum quantization that is used for encoding.
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QInitial: Quantization value used in the first encoded frame. In Constant Q mode this value
shall remain fixed for all frames.
The figures below are the VBR, CBR, and CONSTANT_Q, modes of the H.264 encoder.
