METHOD AND APPARATUS FOR CODING INFORMATION
The invention provides a method and apparatus for coding information that is specifically adapted for smaller presentation formats, such as in a hand held video player. The invention addresses, inter alia, reducing the complexity of video decoding, implementation of an MP3 decoder using fixed point arithmetic, fast YcbCr to RGB conversion, encapsulation of a video stream and an MP3 audio stream into an AVI file, storing menu navigation and DVD subpicture information on a memory card, synchronization of audio and video streams, encryption of keys that are used for decryption of multimedia data, and very user interface (UI) adaptations for a hand held video player that implements the improved coding invention herein disclosed.
1 . A method for reducing the complexity of MPEG4 decoding, comprising the steps of:
disabling intra prediction of AC coefficients, wherein a flag that indicates the need for AC prediction is eliminated from a MPEG4 bitstream;
disabling motion compensation rounding control, wherein truncation is used during motion compensation instead of rounding;
combining VLC decoding and dequantization into one step, wherein dequantization of a coefficient is made immediately after decoding its variable length code, and wherein zero coefficients are excluded from dequantization; and
simplifying inverse discrete cosine transformation with a significance map, wherein said significance map stores positions of last nonzero coefficients in each row/column of a discrete cosine transformation block, wherein said significance map is filled during VLC decoding.
2 . The method of claim 1 , wherein two different versions of inverse discrete cosine transformation are provided: one for rows/columns of eight coefficients and one for rows/columns of three coefficients, and wherein if all coefficients in row/column are zero coefficients, inverse transformation is not performed.
3 . A method for reducing the complexity of MPEG4 decoding, comprising the step of:
disabling intra prediction of AC coefficients, wherein a flag that indicates the need for AC prediction is eliminated from an MPEG4 bitstream.
4 . A method for reducing the complexity of MPEG4 decoding, comprising the step of:
disabling motion compensation rounding control, wherein truncation is used during motion compensation instead of rounding;
5 . A method for reducing the complexity of MPEG4 decoding, comprising the step of:
combining VLC decoding and dequantization into one step, wherein dequantization of a coefficient is made immediately after decoding its variable length code, and wherein zero coefficients are exclude from dequantization.
6 . A method for reducing the complexity of MPEG4 decoding, comprising the step of:
simplifying inverse discrete cosine transformation with a significance map, wherein said significance map stores positions of last nonzero coefficients in each row/column of a discrete cosine transformation block, wherein said significance map is filled during VLC decoding.
7 . The method of claim 6 , wherein two different versions of inverse discrete cosine transformation are provided: one for rows/columns of eight coefficients and one for rows/columns of three coefficients, wherein if all coefficients in row/column are zero coefficients, inverse transformation is not performed.