Video coding system with buffer control quantization step size
AssigneeTeleverket
InventorHarald Brusewitz
Life of this patent
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Abstract
A method and device for image coding, primarily intended to be applied in the transmission of video signals, convert a video signal to a bit stream by coding and quantising. The bit stream is stored in a buffer store before it is sent at a constant bit rate on a transmission line. The content in the buffer store is regulated by varying the step height in the quantiser. With the frame rate at the input being known and the frame rate and bit rate at the output being known, the ideal buffer store content can be determined. The actual buffer store content is sensed and compared with the ideal buffer store content and the difference between these two values is determined. The step height in the quantiser is adjusted as a function of the difference.
Claims5
A method for image coding a video signal having a known frame rate comprising the steps of:
- coding and quantising the video signal to effect digitalisation and compression of the signal to form a bit stream having a bit rate determined by the transmission line on which the bit stream is to be transmitted;
- storing the bit stream in a buffer store, monitoring the content of the buffer store;
- sensing the rate of the bit stream at the output of the buffer store, the ideal buffer store content being as follows
- (GOB-1+MB/33)/12.times.(k1+g)R/fo+bR/fo
- where GOB is the number of the block group,
- MB is the number of the macroblock,
- k1 is the number of skipped frames which are determined by the coder,
- fo is the frame rate of the video signal,
- R is the bit stream rate,
- g takes into account when the coding is terminated, and
- bR/fo is the minimum allowed content in the buffer;
- and
- adjusting the step height in the quantiser as a function of the difference between the monitored and ideal buffer store contents as follows
- QUANT=f(B-Bideal)
- where B is the buffer store content,
- Bideal is the ideal buffer store content, and
- f assumes constant values for intervals of values of B-Bideal and lies within the interval
- QUANTmin.ltoreq.QUANT.ltoreq.QUANTmax
- where QUANTmin and QUANTmax are respectively the minimum and maximum permitted step heights.
A method for image coding a video signal having a known frame rate comprising the steps of:
- coding and quantising the video signal to effect digitalisation and compression of the signal to form a bit stream having a bit rate determined by the transmission line on which the bit stream is to be transmitted;
- storing the bit stream in a buffer store such that
- (GOB-1+MB/33)/12.times.(k1+g)R/fo+bR/fo
- where GOB is the number of the block group,
- MB is the number of the macroblock, k1 is the number of skipped frames, which are determined by the coder,
- fo is the frame rate of the video signal,
- R is the bit stream rate,
- g takes into account when the coding is terminated,
- and bR/fo is the minimum allowed content in the buffer;
- monitoring the content of the buffer store;
- sensing the rate of the bit stream at the output of the buffer store, calculating the ideal buffer store content, and
- adjusting the step height in the quantiser as a function of the difference between the monitored and ideal buffer store contents.
Dependencies are inferred from the claim text.