METHOD AND APPARATUS FOR RATE CONTROL FOR CONSTANT-BIT-RATE-FINITE-BUFFER-SIZE VIDEO ENCODER

• US 20160205402A1
• Filed: 03/18/2016
• Published: 07/14/2016
• Est. Priority Date: 04/18/2000
• Status: Active Grant

• Current Assignee: ATI Technologies ULC (Advanced Micro Devices, Inc.)
• Original Assignee: ATI Technologies ULC (Advanced Micro Devices, Inc.)
• Inventors: Eckart, Stefan
• Granted Patent: US 10,462,473 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• 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 19/152 by measuring the fullness of the transmission buffer
• 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 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/182 the unit being a pixel
• CPC Class Codes: H04N 19/33 in the spatial domain
• CPC Class Codes: H04N 19/423 characterised by memory arrangements H04N19/433 takes precedence
• CPC Class Codes: H04N 19/593 involving spatial prediction techniques
• CPC Class Codes: H04N 19/65 using error resilience

Abstract

A method and apparatus for rate control for a constant-bit-rate finite-buffer-size video encoder is described. Rate control is provided by adjusting the size of non-intra frames based on the size of intra frames. A sliding window approach is implemented to avoid excessive adjustment of non-intra frames located near the end of a group of pictures. A measurement of “power” based on a sum of absolute values of pixel values is used. The “power” measurement is used to adjust a global complexity value, which is used to adjust the sizes of frames. The global complexity value responds to scene changes. An embodiment of the invention calculates and uses L1 distances and pixel block complexities to provide rate control. An embodiment of the invention implements a number of bit predictor block. Predictions may be performed at a group-of-pictures level, at a picture level, and at a pixel block level. An embodiment of the invention resets a global complexity parameter when a scene change occurs.

Claims

1. A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:

obtaining a scene change indication from a prediction error image;

using the scene change indication to reset a global complexity history; and

using the global complexity history to provide the rate control for the video encoder.

2. The method of claim 1 wherein the obtaining the scene change indication from the prediction error image further comprises:

counting a first number of intra-coded pixel block in the prediction error image;

counting a second number of non-intra-coded pixel block in the prediction error image;

calculating a ratio of the first number and the second number;

comparing the ratio to a threshold to determine a result; and

using the result as the scene change indication.

3. Apparatus for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:

a preprocessing stage for determining a power value based on pixel values of only a first frame; and

a group-of-pictures-level rate control block operatively coupled to the preprocessing stage to receive the power value and to provide a target quantizer step size used to provide rate control for the video encoder;

wherein the group-of-pictures-level rate control block causes an adjustment of sizes of non-intra frames based on expected sizes of future intra frames.

4. The apparatus of claim 3 wherein the preprocessing stage updates the power value for each subsequent picture being encoded.

5. Apparatus for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:

a prediction error image block to determine L1 distances according to sums of absolute differences;

a picture-level rate control block operatively coupled to the prediction error image block to receive the L1 distances and to produce a target quantizer step size for a pixel block; and

a complexity estimator block operatively coupled to the prediction error image block to determine non-intra pixel block complexity values and intra pixel block complexity values.

6. A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:

obtaining a prediction error frame including a plurality of pixel-level error values;

calculating a sum of absolute values of the pixel-level error values for a pixel block;

calculating an expected number of bits for the pixel block based on the sum of the absolute values, and

using the expected number of bits for the pixel block to obtain constant-bit-rate video encoding.

7. The method of claim 6 wherein using the expected number of bits for the pixel block to obtain constant-bit-rate video encoding further comprises:

calculating an expected number of bits for a frame in which the pixel block is located; and

using the expected number of bits for the frame to obtain constant-bit-rate video encoding.

8. The method of claim 7 wherein calculating the expected number of bits for the frame further comprises:

summing the expected number of bits for the pixel block for all pixel blocks in the frame.

9. A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising the:

predicting a relationship between a quantizer scale factor and a number of encoded bits of a pixel block based on a known relationship in previous pixel blocks of a same type; and

using the quantizer scale factor to control a pixel block level rate of the video encoder.

10. The method of claim 9 wherein using the quantizer scale factor to control the pixel block level rate of the video encoder further comprises:

using the quantizer scale factor together with a sum of absolute values of pixel-level error values to control the pixel block level rate of the video encoder.

11. The method of claim 9 wherein predicting the relationship between the quantizer scale factor and the number of encoded bits of the pixel block further comprises:

predicting a first relationship between the quantizer scale factor and a first number of encoded bits of a first type of pixel block based on a first known relationship in previous pixel blocks of the first type; and

predicting a second relationship between the quantizer scale factor and a second number of encoded bits of a second type of pixel block based on a second known relationship in previous pixel blocks of the second type.

12. A method for rate control for a constant-bit-rate finite-buffer-size video encoder comprising:

calculating a prediction for a number of bits encoded for a pixel block based on a sum of absolute values of pixel-level error values, a pixel block complexity, and a quantizer scale factor;

using the prediction for adjusting the quantizer scale factor to meet a targeted picture-level number of bits.