Video encoding method and apparatus

• US 20020168012A1
• Filed: 05/14/2002
• Published: 11/14/2002
• Est. Priority Date: 09/10/1999
• Status: Active Grant

• Current Assignee: InterDigital Madison Patent Holdings (InterDigital, Inc.)
• Original Assignee: Thomson Licensing SA (Vantiva SA)
• Inventors: Ramaswamy, Srinath Venkatachalapathy
• Granted Patent: US 6,546,050 B2
• Time in Patent Office: Days
• US Class Current: 375/240.29
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• 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 19/149 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 19/157 Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
• CPC Class Codes: H04N 19/164 Feedback from the receiver or from the transmission channel
• 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 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/197 including determination of the initial value of an encoding parameter H04N19/56 takes precedence
• CPC Class Codes: H04N 19/198 including smoothing of a sequence of encoding parameters, e.g. by averaging, by choice of the maximum, minimum or median value
• CPC Class Codes: H04N 21/23406 involving management of server-side video buffer
• CPC Class Codes: H04N 21/23424 involving splicing one content stream with another content stream, e.g. for inserting or substituting an advertisement
• CPC Class Codes: H04N 21/44004 involving video buffer management, e.g. video decoder buffer or video display buffer
• CPC Class Codes: H04N 21/44016 involving splicing one content stream with another content stream, e.g. for substituting a video clip

Abstract

An exemplary video encoder is disclosed that quantizes pel blocks of a video signal based upon one or more of the following: (i) an actual bit distribution of a previously encoded video frame, (ii) a required decoding delay for a splice point, and (iii) an activity measure of a pel block being encoded. Moreover, an exemplary video encoder uses the above quantization techniques to obtain an encoded video stream having seamless in points and seamless out points. Video encoding methods that utilize the above quantization methods are also disclosed.

Claims

1. A method of encoding a video signal to obtain an encoded video stream having seamless splice points, said encoded video stream having a presentation order and an encode order, said method comprising the steps of:

a) allocating a number of bits to a first group of pictures (GOP) comprising a first plurality of video frames of said video signal that precedes a desired splice point in presentation order;

b) determining an estimated decoding delay for a first video frame of said video signal that follows said desired splice point in encode order;

c) determining a correction factor that is based upon a difference between said estimated decoding delay for said first video frame and a splice point decoding delay, said splice point decoding delay being a delay necessary for said first video frame in order to achieve a seamless splice point at said desired splice point;

d) adjusting said number of bits to allocated to said first GOP based upon said correction factor to obtain an adjusted number of bits for said first GOP; and

e) encoding said first plurality of video frames based upon said adjusted number of bits allocated to said first GOP.

2. The method of claim 1, wherein step c) further comprises the steps of:

c1) determining a total bit adjustment needed in order to achieve a decoding delay for said first video frame that is substantially equal to said splice point decoding delay;

c2) determining a remaining number of GOPs to be encoded before said desired splice point; and

c3) determining said correction factor for said first GOP based upon said total bit adjustment, said remaining number of GOPs, and said number of bits allocated to said first GOP.

3. The method of claim 1, further comprising the steps of:

determining prior to step d), that said first GOP is within a predetermined number of GOPs of said desired splice point.

4. The method of claim 1, wherein step e) further comprises the steps of:

e1) allocating a target number of bits to a second video frame of said first GOP based upon said adjusted number of bits allocated to said first GOP;

e2) obtaining an actual bit distribution indicative of a number of bits used to encode each pel block of a third video frame of said video signal that precedes said second video frame in encode order;

e3) determining a quantization value for a pel block of said second video frame based upon said actual bit distribution of said third video frame and said target number of bits allocated to said second video frame; and

e4) encoding said pel block of said first video frame based upon said quantization value.

5. The method of claim 1, wherein step e) further comprises the steps of:

e1) allocating a target number of bits to a second video frame of said first GOP based upon said adjusted number of bits allocated to said first GOP;

e2) obtaining an actual bit distribution indicative of a number of bits used to encode each pel block of a third video frame of said video signal that precedes said second video frame in encode order;

e3) adjusting said actual bit distribution based upon said target number of bits allocated to said second video frame to obtain a normalized bit distribution in which a total number of bits represented by said normalized bit distribution is substantially equal to said target number of bits allocated to said second video frame;

e4) determining a quantization value for a pel block of said second video frame based upon said normalized bit distribution; and

e5) encoding said pel block of said second video frame based upon said quantization value.

6. A computer readable medium for obtaining an encoded video stream having seamless splice points, said encoded video stream having a presentation order and an encode order, said computer readable medium comprising code which when executed by a video encoder causes said video encoder to:

a) allocate a number of bits to a first group of pictures (GOP) comprising a first plurality of video frames of a video signal that precedes a desired splice point in presentation order;

b) determine an estimated decoding delay for a first video frame of said video signal that follows said desired splice point in encode order;

c) determine a correction factor based upon a difference between said estimated decoding delay for said first video frame and a splice point decoding delay, said splice point delay being a delay necessary for said first video frame to achieve a seamless splice point at said desired splice point;

d) adjust said number of bits to allocated to said first GOP based upon said correction factor; and

e) encode said first plurality of video frames based upon said number of bits allocated to said first GOP.

7. The computer readable medium of claim 6, wherein said code when executed by said video encoder further causes said video encoder to determine said correction factor by:

determining a total bit adjustment needed in order to achieve a decoding delay for said first video frame that is substantially equal to said splice point decoding delay;

determining a remaining number of GOPs to be encoded before said desired splice point; and

determining said correction factor for said first GOP based upon said total bit adjustment, said remaining number of GOPs, and said number of bits allocated to said first GOP.