Method and apparatus for bit rate control in a digital video system

• US 6,263,020 B1
• Filed: 12/24/1996
• Issued: 07/17/2001
• Est. Priority Date: 12/24/1996
• Status: Expired due to Term

• Current Assignee: Mineral Lassen LLC (Intellectual Ventures LLC)
• Original Assignee: Intel Corporation
• Inventors: Lillevold, Karl O., Brucks, Doug, Ing, Stephen, Phomsopha, Key, Gutmann, Michael J., Gardos, Thomas R.
• Primary Examiner(s): Le, Vu
• Application Number:
  US08/773,043
• Time in Patent Office: 1,666 Days
• Field of Search: 348/419, 348/405, 348/400, 348/406, 348/414, 348/417, 348/418, 348/419.1, 375/240.02, 375/240.03, 375/245, 382/251
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/156 Availability of hardware or computational resources, e.g. encoding based on power-saving criteria
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

In a video image compression and transmission system, quantization parameters for a block transform based video compression algorithm can be controlled by a quantizer selector so as to control compressed video frame size. The selection of the appropriate quantization parameter for the nth macroblock of a current frame is based on the cumulative number of compressed bits appearing in the first n-1 macroblocks of a current frame and a previous frame. By controlling the quantization parameter is such a manner, the overall system reacts more quickly to changes in complexity in the video sequence and allocates bits more accurately to different parts of the video frame according to a past history of bit allocation. To efficiently utilize the bandwidth of a transmission medium (such as POTS), a bit count of the contents of the transmit buffer is sent to a buffer regulator in a video controller where it is compared to a low water mark threshold. If the bit count falls below the threshold, an uncompressed video frame is scheduled for compression by a video compressor. By using the low water mark threshold, latency in the overall system is reduced and an efficient use of transmission medium bandwidth is achieved.

Claims

1. A video image compression and transmission system comprising:

a video capture component for generating a video frame represented as N macroblocks, where N is a whole number;

a video compressor coupled to said video capture component for compressing each of said macroblocks according to a quantization parameter;

a quantizer selector coupled to said video compressor and for calculating said quantization parameter for an nth one of said macroblocks for the current frame based on an amount of compressed video image data generated for macroblocks of a previous video frame and an amount of compressed video image data generated for previous macroblocks of the current video frame and supplying said quantization parameter to said video compressor, where n is a whole number.

2. The system of claim 1 wherein said quantizer selector calculates said quantization parameter based further on a target frame size of compressed video image data for the current video frame.

3. The system of claim 2 wherein each of said current and previous video frames includes a succession of rows where each row includes a succession of macroblocks.

4. The system of claim 3 wherein said quantization parameter is prevented from falling below two-thirds of a mean value of said quantization parameter for the previous video frame.

5. The system of claim 3 where said quantization parameter is controlled such that for a current one of said rows, said quantization parameter is held between an upper and a lower limit.

6. The system of claim 1 wherein said quantization parameter for the nth one of said macroblocks based on a cumulative amount of compressed video image data generated for a first n−

1 of said macroblocks of a previous video frame and a first n−

1 of said macroblocks of the current video frame.

7. A video image compression and transmission system comprising:

a video capture component for generating a video frame represented as N macroblocks, where N is a whole number;

a video compressor coupled to said video capture component for compressing each of said macroblocks according to a quantization parameter;

a quantizer selector coupled to said video compressor and for calculating said quantization parameter for an nth one of said macroblocks according to macroblocks of a previous video frame and previous macroblocks of the current video frame and supplying said quantization parameter to said video compressor, where n is a whole number;

a transmit buffer for receiving compressed video data from said video compressor and outputting a byte count value indicating a number of bytes in said transmit buffer; and

a video controller coupled to said video compressor, said video capture component and said transmit buffer, said video controller including a buffer regulator capable of scheduling a compression of an uncompressed video frame by said video compressor when said byte count value falls below a threshold value.

8. A video image compression and transmission system comprising:

a video capture component for generating a video frame including N macroblocks of video data, where N is a whole number;

a video compressor coupled to said video capture component for compressing each of said macroblocks according to a quantization parameter;

a transmit buffer for receiving compressed video data from said video compressor and outputting a bit count value indicating a number of bits in said transmit buffer; and

a buffer regulator coupled to said video compressor and said transmit buffer for scheduling a compression of said video frame by said video compressor when said bit count value falls below a threshold value.

9. A method of compressing video frame data comprising:

(a) generating a succession of video frames at a video capture component, each of said video frames including uncompressed video data;

(b) dividing each video frame into a succession of N macroblocks where each macroblock defines a spatial area of one of said video frames, where N is a whole number;

(c) calculating a quantization parameter value for an nth one of said macroblocks of a current video frame based on an amount of compressed video image data generated for macroblocks of a previous video frame and an amount of compressed video image data generated for previous macroblocks of said current video frame;

(d) compressing said N macroblocks for said current frame into compressed video image data using a block transform based compression method based on said quantization parameter value.

10. A method of compressing video frame data comprising:

(a) generating a succession of video frames at a video capture component, each of said video frames including uncompressed video data;

(b) dividing each video frame into a succession of N macroblocks where each macroblock defines a spatial area of one of said video frames, where N is a whole number;

(c) calculating a quantization parameter value for an nth one of said macroblocks of a current video frame according to macroblocks of a previous video frame and previous macroblocks of said current video frame;

(d) compressing said N macroblocks for said current frame into compressed video image data using a block transform based compression method based on said quantization parameter value.

11. A method of compressing and transmitting video image data in a system including a transmit buffer adapted to receive compressed video image data from a video compressor, the method comprising:

generating a succession of video frame data, each frame including uncompressed video frame data divided into N macroblocks, where each macroblock defines a spatial area of each of said frames and N is a whole number;

outputting a byte count value from said transmit buffer to a video controller, said byte count value indicating a number of bytes in said transmit buffer;

scheduling a compression of one of said succession of video frames by a video controller when said byte count value falls below a threshold value;

compressing said video frame data in a video compressor; and

transferring compressed video frame data from said video compressor to said transmit buffer.

12. The method of claim 11 further comprising:

modifying said threshold value based on said bit count value prior to said transferring step.

13. The method of claim 12 wherein in said modifying step, said threshold value is reduced if said bit count value prior to said transferring step is greater than zero.