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 computational speedup of an Inverse Modified Discrete Cosine Transform (IMDCT) calculation, comprising the step of:
using a simplified multiplication by transform coefficients.
2 . The method of claim 1 , wherein for an IMDCT calculation on 36 and 12 points, transform coefficients with absolute values smaller than 1 are represented in 32.11 format, multiplication is by the coefficient, c:
y =(( x> 5)* c )>>6,
and, wherein for coefficients with absolute values greater than 1 multiplication is by the coefficient, c:
y =(( x>> 5)* c )>>(6− q ).
3 . The method of claim 1 , wherein for an IMDCT calculation on 64 points (synthesis function), where all transform coefficients have absolute value smaller than 1, and are represented in 32.11 format, multiplication is by the coefficient:
y =(( x>> 5)* c )>>6.
4 . The method of claim 1 , wherein for an IMDCT calculation in high precision mode, multiplication is by the coefficient, c:
y=x High* c High+(( x Low* c High+ c Low* x High)>>12).
5 . The method of claim 1 , wherein for an IMDCT calculation in medium and low precision mode, multiplication is by the coefficient, c:
y=x High* c High+(( x Low* c High)>>12).
6 . A method for computational speedup for a final windowing operation in an audio decoder, comprising the steps of:
calculating convolution of output samples by the following methods:
using a scaled transposed window table;
optimizing a convolution loop;
reducing a window table.