Variable rate video encoder

• US 10,027,979 B2
• Filed: 07/21/2015
• Issued: 07/17/2018
• Est. Priority Date: 07/25/2014
• Status: Active Grant

• Current Assignee: Allegro DVT2 Co.
• Original Assignee: Allegro Dvt
• Inventors: Eymery, Pascal, Chong-Pan, Christophe
• Primary Examiner(s): Rahman, Mohammad J
• Application Number:
  US14/805,152
• Publication Number:
  US 20160029042A1
• Time in Patent Office: 1,092 Days
• Field of Search: None
• CPC Class Codes: H04N 19/107 between spatial and temporal predictive coding, e.g. picture refresh
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/577 Motion compensation with bidirectional frame interpolation, i.e. using B-pictures
• CPC Class Codes: H04N 19/593 involving spatial prediction techniques

Abstract

The invention concerns a method of video encoding comprising: determining a first ratio (IP_RATIO) based on previously encoded picture frames of a video sequence comprising one or more intra-coded pictures (I) and one or more predicted pictures (P), the first ratio (IP_RATIO) being calculated based on the ratio between the size of one or more previously encoded intra-coded pictures and the size of one or more previously encoded predicted pictures; and determining a quantization parameter (QP) to be applied to a frame to be encoded based on the first ratio (IP_RATIO).

Claims

1. A method of video encoding comprising:

determining, using a rate control circuit, a first ratio (IPRATIO) based on previously encoded picture frames of a video sequence comprising one or more intra-coded pictures (I) and one or more predicted pictures (P), the first ratio (IPRATIO) being calculated based on the ratio between the size of one or more previously encoded intra-coded pictures and the size of one or more previously encoded predicted pictures;

determining, using the rate control circuit, the size (SSW) of a sliding window of N previously encoded picture frames of the video sequence, the sliding window comprising one or more of the intra-coded pictures and one or more of the predicted pictures, where N is an integer equal to three or more;

determining, using the rate control circuit, a target size (TSW) of the sliding window based on a target size of a group (GOP) of successive pictures comprising a number of pictures from one intra-coded picture up to but not including a subsequent intra-coded picture, the target size being determined based on the following equation;

2. The method of claim 1, wherein the first ratio (IP_RATIO) is determined based on a previous value of the first ratio (PREVIOUS_IP_RATIO) and on a latest ratio between the encoded size of the latest of the intra-coded pictures to be encoded and the latest of the predicted pictures to be encoded.

3. The method of claim 2, wherein the first ratio is determined based on the following equation:

4. The method of claim 1, wherein:

the sliding window further comprises one or more bi-predicted pictures (B); and

determining the target size (T_SW) of the sliding window is further based on a second ratio (PB_RATIO) representing the ratio between the size of one or more of said predicted pictures and the size of one or more of said bi-predicted pictures.

5. The method of claim 1, wherein the target size of the group of successive pictures is determined based on the following equation:

6. The method of claim 1, wherein determining a quantization parameter (QP) to be applied to a frame to be encoded comprises determining a correction factor to be applied to a previous quantization parameter by dividing the size of the sliding window by the target size of the sliding window.

7. The method of claim 6, wherein the quantization parameter has a logarithmic relation with the bitrate, and the quantization parameter is determined by applying the correction factor to a linearized value (QS) determined by linearizing the previous quantization parameter.

8. The method of claim 6, wherein the quantization parameter (NEWQP) is determined based on the following equation:

NEWQP=f_QP(f_QS(OLDQP)×

CORRECTION_FACTOR)

where OLDQP is the previous quantization parameter, CORRECTION_FACTOR is the correction factor, f_QS is a linearization function for linearizing the previous quantization parameter and f_QP is the inverse of the linearization function.

9. A video system comprising:

a rate control circuit configured to;

determine the size (S_SW) of a sliding window of N previously encoded picture frames of the video sequence, the sliding window comprising one or more of the intra-coded pictures and one or more of the predicted pictures, where N is an integer equal to three or more;

determine a target size (T_SW) of the sliding window based on a target size of a group (GOP) of successive pictures comprising a number of pictures from one intra-coded picture up to but not including a subsequent intra-coded picture, the target size being determined based on the following equation;

10. The video system of claim 9, wherein:

the sliding window further comprises one or more bi-predicted pictures (B); and

the rate control circuit is further configured to determine the target size (T_SW) of the sliding window based on a second ratio (PB_RATIO) representing the ratio between the size of one or more of said predicted pictures and the size of one or more of said bi-predicted pictures.

11. The video system of claim 9, wherein the rate control circuit is further configured to determine the first ratio (IP_RATIO) based on a previous value of the first ratio (PREVIOUS_IP_RATIO) and on a latest ratio between the encoded size of the latest of the intra-coded pictures to be encoded and the latest of the predicted pictures to be encoded.