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EP0711079A2
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Method and apparatus for scaling a compressed video bitstream
Assignee: RCA Licensing Corp
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Filing: 1995-10-25
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Granted: —
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Expires: 2015-10-25
Abstract
Abstract A method and apparatus for scaling the bitstream of a compressed video signal includes partial decoding hardware (38, 41) to permit excising of higher frequency AC DCT coefficients or re-quantizing quantized data with a coarser quantization factor. The scaling is performed on a block (macroblock) basis in a manner which linearly scales the amount of compressed data per block. An analyzer (40) generates a profile of cumulative partially decompressed data over a video frame, and bitstream scaling (42) is performed in a manner which insures that a profile of the scaled signal substantially comports with the profile of the original data.
Inventors
- 👤 Wilson Kwok
- 👤 Huifang Sun
- 👤 Joel Walter Zdepski
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-04 06:05
CPC Classifications
H; H04; H04N; H04N19/00; H04N19/40; H04N19/10; H04N19/134; H04N19/146; H04N19/149; H04N19/15; H04N19/60; H04N19/61
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
75 words
Apparatus (38-47) for scaling the bit stream of a compressed video signal which has been compressed on a block basis, said apparatus characterized by an analyzer (40) for determining a cumulative profile of coded bits of said compressed video signal on a block basis, and bit stream scaling means (38, 39, 41,42) responsive to said analyzer for generating a scaled bit stream which is linearly scaled with respect to said profile on said block basis.
Claim 2
Dependent Claim
92 words
The apparatus set forth in claim 1 characterized in that said analyzer comprises: a connection for applying said compressed video signal; a processor coupled to said connection for generating a sum ΣMB i representing a quantity of bits of respective said blocks of said compressed video signal and a further sum ΣΣMB i corresponding to an accumulation of sums ΣMB i of blocks from a first block to block i, and for scaling at least one of said sums ΣΣMB i to produce a signal to control said bit stream scaling apparatus.
Claim 3
Dependent Claim
59 words
The apparatus set forth in claim 2 characterized in that said analyzer scales said sums ΣΣMB i for respective said blocks, and said bit stream scaling apparatus includes a means for selecting quantities of bits of said compressed video signal bits for respective blocks, which quantities are determined for respective blocks according to a corresponding scaled sum ΣΣMB i.
Claim 4
Dependent Claim
42 words
The apparatus set forth in claim 1 characterized in that said bit stream scaling apparatus comprises the cascade connection of a variable length decoder, an inverse quantizer, a quantizer responsive to quantization factors provided by said analyzer, and a variable length encoder.
Claim 5
Dependent Claim
88 words
The apparatus set forth in claim 4 characterized in that said analyzer includes means for forming a profile of bits of codewords of said compressed video signal on a block basis; means for scaling said profile to generate a scaled profile; means for forming a new profile of bits of codewords of compressed video signal provided from said variable length encoder on a block basis; and means for generating quantization factors for controlling quantization of respective said blocks from differences between said scaled profile and said new profile.
Claim 6
Dependent Claim
160 words
The bit stream scaling apparatus set forth in Claim 1, characterized by: a connection for accessing said compressed video signal; said bit stream scaling means includes: a cascade connection of a variable length decoder (38), an inverse quantizer (41), and a quantizer (42), said quantizer having an input port for applying quantization control signal and an output port for providing quantized signal, and said cascade connection being coupled to said connection for accessing said compressed video signal; said analyzer(40) having a first input port coupled to said connection for accessing said compressed video signal, a second input port coupled to said output port of said quantizer (42), and having an output port for providing said quantization control signal, said analyzer generating said quantization control signals for respective said blocks based on differences between a first function of accumulated bits occurring in said compressed video signal and a second function of accumulated bits in signal coupled to said second input port.
Claim 7
Dependent Claim
30 words
The bit stream scaling apparatus set forth in claim 6 characterized in that said analyzer is coupled to the output port of said quantizer with a variable length encoding circuit.
Claim 8
Independent Claim
88 words
A method for reducing the bits in the bitstream of an MPEG coded video signal characterized by: forming (700-710) cumulative sums of bits of macroblocks of said MPEG coded video signal on a macroblock by macroblock basis over an image; forming (712) a scaled version of said cumulative sums; processing (800-809) said MPEG coded video signal such that cumulative sums of bits of macroblocks of processed said MPEG coded video signal on a block by block basis are substantially equivalent to said scaled version of said cumulative sums.
Claim 9
Dependent Claim
20 words
The method set forth in claim 8 characterized in that the step of processing comprises discarding bits of respective macroblocks.
Claim 10
Dependent Claim
73 words
The method set forth in claim 8 characterized in that the step of processing comprises: selecting respective codewords of said MPEG coded video signal from respective macroblocks and forming new cumulative sums of bits of ones of said codewords which were selected on a macroblock by macroblock basis; and terminating the selection of codewords for respective macroblocks when said new cumulative sums of bits are substantially equal to said cumulative sums of bits.
Claim 11
Dependent Claim
97 words
The method set forth in claim 8 characterized in that the step of processing comprises: inverse quantizing quantized codewords of said MPEG coded video signal; quantizing inverse quantized codewords of said MPEG coded video signal with estimated quantizing parameters; forming cumulative sums of bits of macroblocks of said MPEG coded video signal quantized with said estimated quantizing parameters; determining new quantizing parameters, on a macroblock basis, as a function of differences between said scaled version of cumulative sums and said new sums; quantizing inverse quantized codewords of said MPEG coded video signal with said new quantizing parameters.
Claim 12
Dependent Claim
44 words
The method set forth in claim 8 characterized in that the step of forming cumulative sums of bits of macroblocks of said MPEG coded video signal on a macroblock by macroblock basis comprises forming cumulative sums of only bits which represent AC DCT coefficients.
Claim 13
Dependent Claim
68 words
The method set forth in claim 12 characterized in that the step of forming a scaled version comprises: calculating a target value for bits of AC DCT coefficients for respective frames responsive to total bits of said MPEG coded video signal for respective frames; generating a scaling factor equal to the ratio of the target value divided by the cumulative sum for the last macroblock in a frame.
Claim 14
Dependent Claim
80 words
The method set forth in claim 8 characterized in that the step of forming cumulative sums of bits of macroblocks of said MPEG coded video signal on a macroblock by macroblock basis comprises: detecting quantizing values associated with respective macroblocks of said MPEG coded video signal; summing bits of respective codewords for respective macroblocks; and multiplying the sum of bits for a respective macroblock with its associated quantizing value to generate a product of bits summed times the quantizing value.
Claim 15
Dependent Claim
46 words
The method set forth in claim 14 characterized in that the step of forming cumulative sums of bits of macroblocks of said MPEG coded video signal on a macroblock by macroblock basis further comprises, for respective macroblocks forming the sum of preceding and current said products.
Claim 16
Dependent Claim
115 words
The method set forth is claim 15 characterized in that the step of forming a scaled version of said cumulative sums comprises multiplying respective cumulative sums by a factor SF where SF = (1 - %)(ΣΣ MBi ) last - excess Σ(Q MBi (ΣMBi)) last and wherein % is a percentage of bits the bitstream of said MPEG coded video signal is to be reduced, ΣΣ MBilast corresponds to the total bits in a frame, Σ(Q MBi (Σ MBi )) last is a cumulative sum of products of respective quantizing factors times the corresponding sum of bits for respective macroblocks, and excess is the amount by which the previous frame exceeded a desired bit target.
Claim 17
Dependent Claim
154 words
The method set forth in claim 8 characterized in that the step of processing comprises: a) inverse quantizing quantized codewords of said MPEG coded video signal; b) quantizing inverse quantized codewords of a first macroblock of said MPEG coded video signal with an estimated quantizing parameter; c) forming a new sum of bits of said first macroblock quantized with said estimated quantizing parameter; d) determining a new quantizing parameter as a function of the difference between said scaled version of cumulative sums for the current macroblock and said new sum of bits; e) quantizing inverse quantized codewords of a next subsequent macroblock of said MPEG coded video signal with said new quantizing parameter; f) forming a new cumulative sum of bits of all preceding and said next subsequent macroblock quantized with said estimated quantizing parameter or said new quantizing parameter; and g) repeating steps d through f for all remaining macroblocks in a frame.
Claim 18
Dependent Claim
71 words
The method set forth in claim 17 characterized in that the step of determining a new quantizing parameter comprises: generating the difference ΔE between said scaled version of the cumulative sum for a respective macroblock and said new cumulative sum of bits; multiplying the difference ΔE with a gain factor g to generate the product (g)(ΔE); and combining the product (g)(ΔE) with the quantizing factor used to quantize the current macroblock.
Claim 19
Dependent Claim
71 words
The method set forth in claim 11 characterized in that the step of determining a new quantizing parameter comprises: generating the difference ΔE between said scaled version of the cumulative sum for a respective macroblock and said new cumulative sum of bits; multiplying the difference ΔE with a gain factor g to generate the product (g)(ΔE); and combining the product (g)(ΔE) with the quantizing factor used to quantize the current macroblock.
References Cited (Backward Citations)
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