Video encoding control method, video encoding apparatus and video encoding program

• US 9,179,165 B2
• Filed: 04/28/2011
• Issued: 11/03/2015
• Est. Priority Date: 05/07/2010
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Kitahara, Masaki, Shimizu, Atsushi, Ono, Naoki
• Primary Examiner(s): ELAHI, SHAN E
• Application Number:
  US13/695,700
• Publication Number:
  US 20130051456A1
• Time in Patent Office: 1,650 Days
• Field of Search: 375/240.26
• US Class Current: 1/1
• CPC Class Codes: H04N 19/114 Adapting the group of pictures [GOP] structure, e.g. number of B-frames between two anchor frames H04N19/107 takes precedence
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• 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 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/194 involving only two passes
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/80 Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation H04N19/635, H04N19/86 take precedence
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression

Abstract

In a video encoding control method of the present invention, each picture is encoded in units of encoding-order picture groups such as GOPs, and when CPB underflow has occurred, an encoding parameter such as a quantization parameter and filter strength of a pre-filter is changed in such a manner that a generated bit rate is reduced, and an encoding-order picture group that is being encoded is re-encoded from its first picture using the changed encoding parameter.

Claims

1. A video encoding control method performed by a microprocessor operating on executable program steps stored in memory to generate a bit rate and to control the overflow and underflow in a decoder hypothetical buffer and to encode an input video signal, the method comprising the steps of:

sequentially encoding each picture in an encoding-order picture group according to a predetermined encoding parameter, the encoding-order picture group including a predetermined number of pictures and being a collection of pictures successive in an encoding order;

checking if underflow has occurred in the hypothetical buffer based on bit rate information generated in encoding of each picture;

when the underflow has occurred in the hypothetical buffer, changing the encoding parameter in such a manner that a generated bit rate resulting from encoding is reduced and re-encoding the encoding-order picture group that is being encoded from its first picture using the changed encoding parameter,

setting the retry point indicating a position of the picture from which the re-encoding starts based on a maximum inter-picture distance that is a maximum number of pictures capable of being traced back as re-encoding target pictures at the time of re-encoding; and

when encoding of the encoding-order picture group is completed, checking a residual bit rate of the hypothetical buffer, setting the retry point to a first picture in a next encoding-order picture group when the residual bit rate is equal to or greater than a predetermined residual bit rate threshold value, retaining unchanged the retry point when the residual bit rate of the hypothetical buffer is smaller than the predetermined residual bit rate threshold value, and setting the retry point to the first picture in the encoding-order picture group after encoding of the first picture of the next encoding-order picture group is completed without occurrence of the underflow of the hypothetical buffer, wherein;

the step of sequentially encoding includes sequentially encoding each picture in the encoding-order picture group according to an encoding parameter set according to a retry count indicating the number of times of re-encoding,

the step of re-encoding includes incrementing the retry count when the underflow has occurred in the hypothetical buffer and changing the encoding parameter into an encoding parameter with which the generated bit rate resulting from encoding is reduced as a value of the retry count increases.

2. The video encoding control method according to claim 1, comprising a step of checking a residual bit rate of the hypothetical buffer when the underflow has not occurred in the hypothetical buffer until encoding of a last picture in the encoding-order picture group is completed, not changing the value of the retry count when the residual bit rate is smaller than a predetermined residual bit rate threshold value or the retry count is 0, and decrementing the retry count when the residual bit rate is equal to or greater than the residual bit rate threshold value and the retry count is not 0.

3. The video encoding control method according to claim 1, comprising a step of decrementing the retry count when the underflow has not occurred in the hypothetical buffer until encoding of a last picture in the encoding-order picture group is completed.

4. The video encoding control method according to claim 1, wherein:

the encoding parameter is a quantization parameter, filter strength of a pre-filter for the input video signal, or both of the quantization parameter and the filter strength,

when the encoding parameter is the quantization parameter, the encoding parameter in which a step size of the quantization parameter increases as the value of the retry count increases is set, and

when the encoding parameter is the filter strength of the pre-filter, the encoding parameter in which a blurring degree by a filtering process increases as the value of the retry count increases is set.

5. The video encoding control method according to claim 1, wherein when the underflow has not occurred in the hypothetical buffer until encoding of a last picture in the encoding-order picture group is completed in re-encoding of the encoding-order picture group, an encoding parameter used to encode a next encoding-order picture group restores to an encoding parameter value at the time of normal encoding.

6. The video encoding control method according to claim 1, wherein:

when the underflow has not occurred in the hypothetical buffer until encoding of a last picture in the encoding-order picture group is completed in re-encoding of the encoding-order picture group, a residual bit rate of the hypothetical buffer is checked,

an encoding parameter used to encode the next encoding-order picture group is not changed when the residual bit rate is smaller than a predetermined residual bit rate threshold value, and

the encoding parameter restores to an encoding parameter value at the time of normal encoding when the residual bit rate is equal to or greater than the predetermined residual bit rate threshold value.

7. The video encoding control method according to claim 1, wherein:

the encoding parameter is a quantization parameter, filter strength of a pre-filter for the input video signal, or both of the quantization parameter and the filter strength, and

the encoding parameter is changed to increase a step size of the quantization parameter at the time of re-encoding when the encoding parameter is the quantization parameter and to increase a blurring degree by a filtering process when the encoding parameter is the filter strength of the pre-filter, at the time of re-encoding of the encoding-order picture group.

8. A video encoding apparatus in which a generated bit rate is controlled so that a hypothetical buffer in a decoder does not collapse and an input video signal is encoded, the apparatus comprising:

an encoding device that sequentially encodes each picture of an encoding-order picture group according to a predetermined encoding parameter, the encoding-order picture group including a predetermined number of pictures and being a collection of pictures successive in an encoding order;

a buffer management device that checks if underflow has occurred in the hypothetical buffer based on bit rate information generated in encoding of each picture and output retry information when detecting that the underflow has occurred in the hypothetical buffer;

a parameter adjustment device that changes the encoding parameter in such a manner that a generated bit rate resulting from encoding is reduced when the retry information is output and signal the encoding device of the changed encoding parameter;

a buffer state prediction device that checks a residual bit rate of the hypothetical buffer when encoding of the encoding-order picture group is completed and determines whether the residual bit rate is equal to or greater than a predetermined residual bit rate threshold value; and

a retry point management device that sets the retry point to a first picture in a next encoding-order picture group when the residual bit rate of the hypothetical buffer is equal to or greater than the predetermined residual bit rate threshold value according to a determination result of the buffer state prediction device, retaining unchanged the retry point when the residual bit rate of the hypothetical buffer is smaller than the predetermined residual bit rate threshold value, and to set the retry point to the first picture in the encoding-order picture group after encoding of the first picture in the next encoding-order picture group is completed without occurrence of underflow of the hypothetical buffer, wherein

when the retry information is output, the encoding device re-encodes the input video signal from a first picture in the encoding-order picture group that is being encoded, using the encoding parameter changed by the parameter adjustment device, and the encoding device sequentially encodes each picture of the encoding-order picture group according to an encoding parameter set according to a retry count indicating the number of times of re-encoding;

the video encoding apparatus includes a retry count management device that increments the retry count when the retry information is output and that decrements the retry count when the retry information output is deferred until encoding of a last picture in the encoding-order picture group is completed,

the parameter adjustment device sets an encoding parameter with which a generated bit rate resulting from encoding is reduced as a value of the retry count increases, and notifies the encoding device of the set encoding parameter, the encoding parameter being determined according to the retry count, and

the encoding device re-encodes the input video signal from the first picture in the encoding-order picture group set as the retry point using the encoding parameter changed by the parameter adjustment device when the retry information is output.

9. The video encoding apparatus according to claim 8, comprising a buffer state prediction device that checks a residual bit rate of the hypothetical buffer when the encoding of a last picture in the encoding-order picture group is completed without occurrence of the underflow in the hypothetical buffer, and output parameter change/non-change information indicating whether a parameter change is required according to whether the residual bit rate is equal to or greater than a predetermined residual bit rate threshold value,

wherein, when the retry count management device receives the parameter change/non-change information from the buffer state prediction device, the retry count management device does not change the value of the retry count when the parameter change/non-change information indicates that the parameter change is not required or the retry count is 0, and decrements the retry count when the parameter change/non-change information indicates that the parameter change is required and the retry count is not 0.

10. A video encoding apparatus that generates a bit rate and controls the overflow and underflow in a decoder hypothetical buffer and that encodes an input video signal, the apparatus comprising:

an encoding device that sequentially encodes each picture in an encoding-order picture group according to a predetermined encoding parameter, the encoding-order picture group including a predetermined number of pictures and being a collection of pictures successive in an encoding order;

a buffer management device that checks if underflow has occurred in the hypothetical buffer based on bit rate information generated in encoding of each picture, and output retry information when detecting that the underflow has occurred in the hypothetical buffer;

a parameter adjustment device that changes the encoding parameter in such a manner that a generated bit rate resulting from encoding is reduced when the retry information is output, and signal the encoding device of the changed encoding parameter; and

a retry point management device that sets a retry point indicating a position of the picture from which the re-encoding starts based on a maximum inter-picture distance that is a maximum number of pictures capable of being traced back as re-encoding target pictures at the time of re-encoding,

wherein the encoding device re-encodes the input video signal from the picture set as the retry point in the encoding-order picture group that is being encoded using the encoding parameter changed by the parameter adjustment device when the retry information is output.

11. A non-transitory computer-readable recording medium which stores video encoding program for causing a computer to execute a video encoding control method comprising the steps of:

sequentially encoding each picture in an encoding-order picture group according to a predetermined encoding parameter, the encoding-order picture group including a predetermined number of pictures and being a collection of pictures successive in an encoding order;

checking if underflow has occurred in a hypothetical buffer based on bit rate information generated in encoding of each picture;

when the underflow has occurred in the hypothetical buffer, changing the encoding parameter in such a manner that a generated bit rate resulting from encoding is reduced and re-encoding the encoding-order picture group that is being encoded from its first picture using the changed encoding parameter;

setting the retry point indicating a position of the picture from which the re-encoding starts based on a maximum inter-picture distance that is a maximum number of pictures capable of being traced back as re-encoding target pictures at the time of re-encoding; and

when encoding of the encoding-order picture group is completed, checking a residual bit rate of the hypothetical buffer, setting the retry point to a first picture in a next encoding-order picture group when the residual bit rate is equal to or greater than a predetermined residual bit rate threshold value, not changing the retry point when the residual bit rate of the hypothetical buffer is smaller than the predetermined residual bit rate threshold value, and setting the retry point to the first picture in the encoding-order picture group after encoding of the first picture of the next encoding-order picture group is completed without occurrence of the underflow of the hypothetical buffer, wherein;

the step of sequentially encoding includes sequentially encoding each picture in the encoding-order picture group according to an encoding parameter set according to a retry count indicating the number of times of re-encoding,

the step of re-encoding includes incrementing the retry count when the underflow has occurred in the hypothetical buffer and changing the encoding parameter into an encoding parameter with which the generated bit rate resulting from encoding is reduced as a value of the retry count increases.