Abstract: Video compression systems often use motion compensation to compress the data. Motion compensation systems usually use motion vectors to represent motion. A multipass motion vector determination unit is introduced that makes more then one pass to select a motion vector. The multipass motion vector determination unit first examines an initial search window area around each macroblock to select a first motion vector for each macroblock. The multipass motion vector determination unit then determines a second search window for each macroblock based upon the first motion vector found for that macroblock. Specifically, the second search window consist of an area located in the direction of the first motion vector. A second motion vector is selected from the second search window. Additional motion vectors may similarly be selected.

Abstract: Optimizing the encoding time for a variable length coding unit involves allowing the 8.times.8 blocks to be processed consecutively. Thus, a method and apparatus that allows for efficient processing of the 8.times.8 blocks consecutively is required. A method and apparatus is provided that generates variable length code (VLC) data without requiring buffer memory for storing coefficient data temporarily or special circuitry for generating end-of-block (EOB) Codes. An input code is received. The input code includes an end-of-block (EOB) indicator, a zero run-length, and a coefficient level. The input code is converted into a corresponding VLC and the VLC is output. The input code is converted into the corresponding VLC by: (1) Forming an address based upon the EOB indicator, the zero run-length, and the coefficient level. For example, the EOB indicator may be the most significant bit of the address, followed by the zero run-length, and the least significant portion of the address may be the coefficient level.

Abstract: A method of implementing a fast video encoder by approximating a frame motion vector is introduced. MPEG-2 encoding uses both field and frame vectors in the encoding process. To implement an encoder in an efficient manner, an approximated motion vector created from two field motion vectors is used. The frame motion vector may be determined using the two field motion vectors alone, or by using the two field motion vectors in conjunction with their respective absolute error values. By using the disclosed methods, a motion estimation part for generating frame motion vector is not necessary. Only two field motion estimation parts are required to determine the field motion vectors, the frame motion vector is then approximated using the two field motion vectors. The cost and complexity of a digital video encoder system is thereby reduced.

Abstract: A method and apparatus for efficient motion vector detection is disclosed that provides an expanded search window with a plurality of motion processors. The internal search window of each motion processor is arranged as a set of N row by M column rectangular subblocks. An address generator circuit scans a stream of pixel data values out of a reference frame memory while a set of delay circuits route the stream of pixel data values to the input paths for the internal subblocks and match input timing for the motion processors.

Abstract: MPEG encoded video requires the data to be variable length coded. To perform the variable length coding, most MPEG encoders use a ROM array. To reduce the cost of implementing a variable length coding unit a method of reducing the number of Read Only Memory (ROM) units required to implement the encoder is introduced. Specifically, a variable length encoder that outputs smaller incomplete variable length codes in a few rare instances. Since smaller variable length codes are output, the number of Read Only Memory (ROM) units in the Read Only Memory array can be reduced. The smaller incomplete variable length codes are later made complete using length information.

Abstract: A motion vector detecting apparatus for detecting motion vectors based on a current frame data and the preceding frame data. In the motion vector detecting apparatus, first and second memories are provided in order to store the current frame data and the preceding frame data. Additionally, a number of first cache memories, a number of second cache memories, a control circuit, and a motion vector calculation circuit are provided. The control circuit selects the input cache memories into which pixel data are to be written, and the output cache memories, from which pixel data are to be read out, from the first and second cache memories, so that the input cache memories and the output cache memories have no redundant cache memory. Pixel data corresponding to the detection image blocks stored in the first memory and pixel data corresponding to the search image blocks stored in the second memory are sequentially written in the selected input cache memories of the first and second cache memories.