Rate Control for a Multimedia Compression and Encoding System

Abstract

A rate controller for allocating a bit budget for video frames to be encoded is disclosed. The rate controller of the present invention considers many different factors when determining the frame bit budget including: desired video quality, target bit rate, frame type (intra-frame or inter-frame), frame duration, intra-frame frequency, frame complexity, intra-block frequency within an intra-frame, buffer overflow, buffer underflow, and the encoded video frame quality for a possible second pass.

1 . A method of encoding digital video information into a bit stream, said method comprising:
 determining a default bit budget for a video frame to be digitally encoded into said bit stream;   examining a plurality of factors related to said video frame or said bit stream; and   adjusting said default bit budget according to said plurality of factors to generate a target bit budget for said video frame.   
   
   
       2 . The method as claimed in  claim 1  wherein said default bit budget is based upon a frame ratio. 
   
   
       3 . The method as claimed in  claim 2  wherein said frame ratio is relative to an average frame size. 
   
   
       4 . The method as claimed in  claim 2  wherein said frame ratio is determined by a video image quality level. 
   
   
       5 . The method as claimed in  claim 4  wherein said video image quality level is based upon a bits per pixel per frame value. 
   
   
       6 . The method as claimed in  claim 5  wherein said bits per pixel per frame value is calculated by
 generating an intermediate result by dividing a bit rate by a width times height of said video frame; and   multiplying said intermediate result by an average frame duration.   
   
   
       7 . The method as claimed in  claim 6  wherein said bit rate comprises a channel bandwidth. 
   
   
       8 . The method as claimed in  claim 6  wherein said bit rate comprises a media read bit rate. 
   
   
       9 . The method as claimed in  claim 1  wherein said default bit budget is dependent on a frame type. 
   
   
       10 . The method as claimed in  claim 9  wherein said frame type may be an intra-frame or an inter-frame. 
   
   
       11 . The method as claimed in  claim 2  wherein said frame ratio is dependent on a frame type. 
   
   
       12 . The method as claimed in  claim 11  wherein said frame type may be an intra-frame or an inter-frame. 
   
   
       13 . The method as claimed in  claim 3  wherein said average frame size comprises a historical weighted average. 
   
   
       14 . The method as claimed in  claim 1  wherein one of said plurality of factors comprises a memory buffer condition. 
   
   
       15 . The method as claimed in  claim 14  wherein said memory buffer condition comprises a ratio between a current buffer condition and a warning buffer condition. 
   
   
       16 . The method as claimed in  claim 14  wherein said memory buffer condition comprises a buffer underflow warning condition. 
   
   
       17 . The method as claimed in  claim 14  wherein said memory buffer condition comprises a buffer overflow warning condition. 
   
   
       18 . The method as claimed in  claim 1  wherein said one of said plurality of factors comprises a video frame duration. 
   
   
       19 . The method as claimed in  claim 18  wherein said video frame duration comprises a weighted historical average. 
   
   
       20 . The method as claimed in  claim 1  wherein one of said plurality of factors comprises a video frame complexity. 
   
   
       21 . The method as claimed in  claim 20  wherein said video frame complexity comprises a mean average difference (MAD) for said video frame. 
   
   
       22 . The method as claimed in  claim 21  wherein said mean average difference (MAD) comprises a mean of sum of absolute differences (SAD). 
   
   
       23 . The method as claimed in  claim 1  wherein one of said plurality of factors comprises an intra-block frequency in said video frame. 
   
   
       24 . A method of encoding digital video information into a bit stream, said method comprising:
 examining a plurality of factors related to said bit stream or a next video frame in said bit stream; and   setting a bit budget for said next video frame to be digitally encoded into said bit stream wherein said bit budget is dependent upon said plurality of factors.   
   
   
       25 . The method as claimed in  claim 24  wherein said bit budget is comprises of a default bit budget that is subsequently adjusted. 
   
   
       26 . The method as claimed in  claim 25  wherein said default bit budget is based upon a frame ratio. 
   
   
       27 . The method as claimed in  claim 26  wherein said frame ratio is relative to an average frame size. 
   
   
       28 . The method as claimed in  claim 26  wherein said frame ratio is determined by a video image quality level. 
   
   
       29 . The method as claimed in  claim 28  wherein said video image quality level is based upon a bits per pixel per frame value. 
   
   
       30 . The method as claimed in  claim 29  wherein said bits per pixel per frame value is calculated by
 generating an intermediate result by dividing a bit rate by a width times height of said video frame, and   multiplying said intermediate result by an average frame duration.   
   
   
       31 . The method as claimed in  claim 30  wherein said bit rate comprises a channel bandwidth. 
   
   
       32 . The method as claimed in  claim 30  wherein said bit rate comprises a media read bit rate. 
   
   
       33 . The method as claimed in  claim 24  wherein said wherein one of said plurality of factors comprises a frame type. 
   
   
       34 . The method as claimed in  claim 33  wherein said frame type may be an intra-frame or an inter-frame. 
   
   
       35 . The method as claimed in  claim 26  wherein said frame ratio is dependent on a frame type. 
   
   
       36 . The method as claimed in  claim 35  wherein said frame type may be an intra-frame or an inter-frame. 
   
   
       37 . The method as claimed in  claim 37  wherein said average frame size comprises a historical weighted average. 
   
   
       38 . The method as claimed in  claim 24  wherein one of said plurality of factors comprises a memory buffer condition. 
   
   
       39 . The method as claimed in  claim 38  wherein said memory buffer condition comprises a ratio between a current buffer condition and a warning buffer condition. 
   
   
       40 . The method as claimed in  claim 38  wherein said memory buffer condition comprises a buffer underflow warning condition. 
   
   
       41 . The method as claimed in  claim 38  wherein said memory buffer condition comprises a buffer overflow warning condition. 
   
   
       42 . The method as claimed in  claim 24  wherein one of said plurality of factors comprises a video frame duration. 
   
   
       43 . The method as claimed in  claim 42  wherein said video frame duration comprises a weighted historical average. 
   
   
       44 . The method as claimed in  claim 24  wherein one of said plurality of factors comprises a video frame complexity. 
   
   
       45 . The method as claimed in  claim 44  wherein said video frame complexity comprises a mean average difference (MAD) for said video frame. 
   
   
       47 . The method as claimed in  claim 45  wherein said mean average difference (MAD) comprises a mean of sum of absolute differences (SAD). 
   
   
       48 . The method as claimed in  claim 24  wherein one of said plurality of factors comprises an intra-block frequency in said next video frame.