Method and apparatus for performing motion compensation on video data

Abstract

An apparatus and method for performing two-pass real time video compression is provided. Tactical decisions such as encoding and quantization values are determined in software, whereas functional execution steps are performed in hardware. By appropriately apportioning the tasks between software and hardware, the benefits of each type of processing are exploited, while minimizing both hardware complexity and data transfer requirements. One key concept that allows the compression unit to operate in real time is that the architecture and pipelining both allow for B frames to be executed out of order. By buffering B frames, two-pass motion estimation techniques can be performed to tailor bit usage to the requirements of the frame, and therefore provide a more appealing output image.

Description

RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10 / 721,947 filed on Nov. 25, 2003 which is a divisional of U.S. patent application Ser. No. 09 / 613,359 filed Jul. 10, 2000 (now U.S. Pat. No. 6,760,478 issued Jul. 6, 2004) which is a continuation of U.S. patent application Ser. No. 08 / 670,199 filed on Jun. 21, 1996 (now U.S. Pat. No. 6,101,275 issued Aug. 8, 2000), the entire teachings of which are incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention relates in general to computer systems and more specifically to computer video compression and decompression techniques. BACKGROUND OF THE INVENTION [0003] With the convergence of computers, communications and media, video compression techniques have become increasingly important. Video compression is often used to translate video images (from camera, VCR, laser discs, etc.) into digitally encoded frames. The digitally encoded frames may then be easily transferred o...

AI Technical Summary

Benefits of technology

[0016] With such and arrangement, a high quality image may be produced because bits are more optimally allocated across pictures than they are using conventional techniques. Because the reference frame is encoded prior to the dependent frames, such as B frames, more bits are available to encode the reference frame. It is inherently more important for reference frames to be optimally encoded because the reference frame is not only displayed but is used to effect encoding of up to 4 other dependent frames. Accordingly, the present invention, by delaying the compression of dependent frames until all associated reference frames have been compressed, provides a high quality image.

[0017] According to a further aspect of the invention, the method of compressing the frames further includes the steps of determining motion characteristics for each of said frames and providing compressed data for each of the frames in response to the motion characteristics. In the present invention, the step of determining motion characteristics operates on a first frame in parallel with the step of providing compressed data operating on a second frame. With such an arrangement, the motion characteristic stage and the data compression stage each can be designed to process a frame in one frame interval. As a result, a fully pipelined operation may be provided that allows for real time two-pass video compression.

[0018] According to a further aspect of the invention, the method includes the step of storing the dependent, B frames in a memory of a coupled computer system while they await processing of their associated reference frames. Such an arrangement minimizes the storage requirements of the video compression / decompression unit itself, thereby reducing the overall cost of the system.

Problems solved by technology

One drawback of this scheme arises from the fact that only a fixed number of bits are allocated for encoding a frame.

However the complexity of the process has precluded it from being a valuable tool for video compression applications which require real-time performance.

The main problem with two-pass compression techniques is encountered when analyzing B frames, as will be shown below.

As seen in FIG. 1, a problem with real-time two pass processing soon develops when encoding B frames.

Although the ME stage is free, the B2 frame may not be input for ME processing, because the data for the next P frame has not yet been calculated.

If the processing of the P7 frame is extended to time T7, then the compression engine is no longer operating in real time, and thus the prior art solution is ineffective at providing a real-time two-pass compression algorithm.

However, such a solution would require more process power than is currently marketable for video compression techniques.

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