Video compression and transmission techniques
Embodiments feature families of rate allocation and rate control methods that utilize advanced processing of past and future frame/field picture statistics and are designed to operate with one or more coding passes. At least two method families include: a family of methods for a rate allocation with picture look-ahead; and a family of methods for average bit rate (ABR) control methods. At least two other methods for each method family are described. For the first family of methods, some methods may involve intra rate control. For the second family of methods, some methods may involve high complexity ABR control and/or low complexity ABR control. These and other embodiments can involve any of the following: spatial coding parameter adaptation, coding prediction, complexity processing, complexity estimation, complexity filtering, bit rate considerations, quality considerations, coding parameter allocation, and/or hierarchical prediction structures, among others.
1. A method for rate control, comprising:
determining a bit target, and a number of bits used;
determining a rate factor associated with each of a plurality of previously coded frames;
for each rate factor associated with each of the plurality of previously coded frames, determining an absolute difference between the bit target and a number of bits that would have been used if each rate factor was used to obtain the quantization parameters for each of the previously coded frames;
selecting a minimum value from the absolute differences to obtain a current rate factor;
obtaining a current quantization parameter based on the current rate factor and a complexity value of a current frame; and
encoding the current frame using the current quantization parameter.
2. The method of claim 1 , further comprising:
determining a quantization parameter modifier based on the number of bits used, wherein the quantization parameter modifier modifies the current quantization parameter to correct over-utilization or under-utilization of a bit budget, before encoding the current frame.
3. A method for rate control, comprising:
initializing values for a coding parameter, a rate factor, wherein the values for the coding parameter comprise variable weights for each frame that are variable in time or variable in a number of bits;
determining a bit target, and a number of bits used;
determining, for a current frame, a rate factor with a function of the bit target and a sum of a complexity, wherein the sum of the complexity is based on a sum of a one or more complexity values, wherein each of the one or more complexity values is associated with a previously coded frame, and wherein each of the one or more complexity values is based on a function of: (i) a number of bits used to code the associated previously coded frame, (ii) a quantization step size used to code the associated previously coded frame, (iii) a priority level, and (iv) a complexity value of a frame coded before the associated previously coded frame;
obtaining a current quantization parameter based on the rate factor and a complexity value of the current frame; and
encoding the current frame using the current quantization parameter.
4. The method of claim 3 , further comprising:
determining an overflow parameter based on the bit target and the number of bits used, wherein the overflow parameter modifies the current quantization parameter value to correct over-utilization or under-utilization of a buffer before encoding the current frame.
5. The method of claim 4 , further comprising
filtering complexities using the weights; and
deriving one or more coding parameters from the filtered complexities.
6. The method of claim 4 , wherein the method further comprises:
estimating complexity;
coding a frame; and
after coding the frame, adding the estimate of complexity to a sum of other complexities and weighing a resultant complexity according to a prediction type, a picture type, or a scene type.