2.2.3.2 Mode B
The H.263 mode B payload header, which consists of 8 bytes and starts at the luminance boundaries without the PB-frames option.
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1 |
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2 |
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3 |
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F |
P |
SBIT |
EBIT |
SRC |
QUANT |
I |
A |
S |
GOBN |
MBA |
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HMV1 |
VMV1 |
HMV2 |
VMV2 |
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F (1 bit): The mode of the payload header. This value MUST be one.
P (1 bit): Optional PB-frames mode as defined by the H.263. This value MUST be zero.
SBIT (3 bits): The start bit position, which specifies the number of bits to be ignored in the first data byte, starting with the most significant.
EBIT (3 bits): The end bit position, which specifies the number of bits to be ignored in the last data byte, starting with the least significant.
SRC (3 bits): The source format specifies the resolution of the current picture.
QUANT (5 bits): Quantization value for the first macro block (MB) coded at the start of the packet. Set to zero if the packet begins with a GOB header.
I (1 bit): Picture coding type.
-
Value
Meaning
0
Intercoded.
1
Intracoded.
A (1 bit): This value MUST be zero.
S (1 bit): This value MUST be zero.
GOBN (5 bits): The group of blocks number (GOBN) value is defined by the inherent resolution.
MBA (1 byte): The address within the GOB of the first MB in the packet, counting form zero in scan order.
HMV1 (1 byte): Horizontal vector predictor for the first MB in this packet.
VMV1 (1 byte): Vertical vector predictor for the first MB in this packet.
HMV2 (1 byte): Horizontal motion vector predictors for the third MB in this packet.
VMV2 (1 byte): Vertical motion vector predictors for the third MB in this packet.