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 fast fixed-point implementation of an MPEG-1 Layer 3 audio decoding algorithm, comprising the steps of:
representing data as a sum of high and low parts:
y=x High* c High+(( x Low* c High+ c Low* x High)>>12)+(( x Low* c Low)>>24);
and
removing small parts from said sum.
2 . The method of claim 1 , comprising a high precision summing step as follows:
y=x High* c High+(( x Low* c High+ c Low* x High)>>12).
3 . The method of claim 1 , comprising a medium and low precision step as follows:
y=x High* c High+(( x Low* c High)>>12).
4 . The method of claim 1 , comprising a simplified multiplication on constant coefficients in 32.24 representation implemented as:
y =(( x>> 6)* c )>>6,
in assumption that
|c float |<1;
wherein if
1.0<|c float |<2.0,
said multiplication is performed as
y =(( x>> 6)* c )>>5
where
c =(int)( c float *(1<<12)+0.5)
wherein if
1.0 <|c float |<(1<< q ),
using multiplication in a form:
y =(( x>> 6)* c )>>(6− q )
where
c =(int)( c float *(1<<(12− q ))+0.5).