Video coding architecture and methods for using same

A method of coding a switching picture S.sub.12 for switching from a first bitstream having a SP-picture S.sub.1 to a second bitstream having a second SP-picture S.sub.2, said method comprising the steps of:

• copying the bitstream of the intra macroblocks in second SP-picture S.sub.2 to switching picture S.sub.12;
• and
• encoding remaining macroblocks comprising the steps of:
• forming a predicted frame for S.sub.12 by performing motion estimation with a plurality of reference pictures which are preceding S.sub.1 in said first bitstream;
• calculating a set of transform coefficients for predicted image c.sub.pred by performing a forward transform;
• quantizing the obtained transform coefficients to resulting in quantized coefficient levels;
• and
• subtracting said quantized coefficient levels from a set of corresponding coefficient levels of said second SP-picture S.sub.2.

A decoder for decoding encoded data wherein identical frames may be obtained even when they are predicted using different reference frames, said decoder comprising:

• means for forming a prediction block P of a current block of data I using a plurality of motion vectors and a reference frame;
• means for calculating a plurality of transform coefficients c.sub.pred for said prediction block;
• means for calculating a plurality of quantized reconstruction coefficients I.sub.rec for said current block of data, wherein
• I.sub.rec=(c.sub.pred×A(QP1)+I.sub.err×F(QP1,QP2)+f×220)//220 where F(QP1,QP2)=(220×A(QP1)+0.5×A(QP2))//A(QP2);
• means for dequantizing said plurality of quantized reconstruction image coefficients, creating a plurality of dequantized coefficients d.sub.rec;
• and
• means for inverse transforming said plurality of dequantized coefficients.

A decoder for decoding a block of encoded data wherein identical frames may be obtained even when they are predicted using different reference frames, said decoder comprising:

• frame memory for storing a reference frame;
• demultiplexer for receiving and demultiplexing said encoded data into motion information and current frame information;
• motion compensation predictor coupled to said demultiplexer and said frame memory for receiving said motion information and constructing a prediction of the current block based on said motion information and reference frame;
• transformer coupled to said motion compensation predictor for creating a plurality of transform coefficients;
• quantizer coupled to said transformer for quantizing said plurality of coefficients;
• adder coupled to said quantizer and said demultiplexer for adding current frame information and said quantized plurality of coefficients to form a plurality of coefficients for a reconstructed frame;
• inverse quantizer coupled to said adder;
• and
• inverse transformer coupled to said inverse quantizer.

A method for decoding a frame of video data, comprising the steps of:

• forming a prediction of a current block of data using a plurality of motion vectors and a reference frame creating a predicted block;
• calculating a plurality of transform coefficients c.sub.pred from said predicted block;
• calculating a plurality of quantized reconstruction coefficients I.sub.rec for said current block of data using
• I.sub.rec=(c.sub.pred×A(QP1)+I.sub.err×F(QP1,QP2)+f×220)//220, wherein F(QP1,QP2)=(220×A(QP1)+0.5×A(QP2))//A(QP2);
• dequantizing said plurality of quantized reconstruction image coefficients, creating a plurality of dequantized coefficients d.sub.rec;
• and
• inverse transforming said plurality of dequantized coefficients.

A method for decoding a frame of video data, comprising the steps of:

• forming a prediction of a current block of data using a plurality of motion vectors and a reference frame creating a predicted block;
• calculating a plurality of transform coefficients c.sub.pred from said predicted block;
• calculating reconstruction image coefficients c.sub.rec wherein
• c.sub.rec=c.sub.pred+alpha(QP2)×I.sub.err, wherein alpha(QP2) is a quantization parameter dependent on the method of quantization and used QP value;
• and
• quantizing said reconstruction coefficients creating a plurality of quantized reconstructed image coefficients I.sub.rec;
• dequantizing said plurality of quantized reconstruction image coefficients, creating a plurality of dequantized coefficients d.sub.rec;
• and
• inverse transforming said plurality of dequantized coefficients.

An encoder for encoding a frame of video data, comprising the steps of:

• means for forming a prediction of a current block of data using a plurality of motion vectors and a reference frame;
• means for calculating a plurality of transform coefficients c.sub.orig for said current block of data corresponding to a set of basis functions;
• means for calculating a plurality of transform coefficients c.sub.pred for said predicted block;
• means for quantizing said predicted block coefficients using quantization parameter QP=QP1 creating a plurality of quantized prediction image coefficients;I.sub.pred.
• means for calculating the prediction error coefficients using
• c.sub.err=c.sub.orig−I.sub.pred×alpha(QP1)
• wherein alpha(QP1)=(220+0.5×A(QP1))//A(QP1);
• and
• means for quantizing said prediction error coefficients.

A method for encoding a frame of video data, comprising the steps of:

• forming a prediction of a current block of data using a plurality of motion vectors and a reference frame;
• means for calculating a plurality of transform coefficients c.sub.orig for said current block of data corresponding to a set of basis functions;
• calculating a plurality of transform coefficients c.sub.pred for said predicted block;
• quantizing said predicted block coefficients using quantization parameter QP=QP1 creating a plurality of quantized prediction image coefficientsI.sub.pred;
• calculating the prediction error coefficients using:
• c.sub.err=c.sub.orig−I.sub.pred×alpha(QP1);
• wherein alpha(QP1)=(220+0.5×A(QP1))//A(QP1);
• and
• quantizing said prediction error coefficients.

A method for enabling access in a data stream, said method comprising the steps of:

• placing a plurality of SP-pictures at fixed intervals within a first bitstream;
• generating an I-picture and an SP-picture for each one of said plurality of SP-pictures in said first bitstream;
• storing said I-picture in a second bitstream at a temporal location preceding said each one of said plurality of SP-pictures in said first bitstream;
• and
• storing said SP-picture in said second bitstream at same temporal locations as each of said SP-pictures in said first bitstream.

A method for providing Video Redundancy Coding (VRC), comprising the steps of:

• dividing a sequence of pictures into a plurality of threads wherein all pictures are assigned to one of said plurality of threads in a round-robin fashion;
• coding each of said plurality of threads independently;
• creating a SP-picture, wherein all of said threads converge;
• and
• starting a second plurality of threads from said SP-picture.

A method for providing error control in a data stream between a sender and a client in a communication system, said method comprising:

• creating a plurality of representations of a picture in the form of a plurality of SP-pictures predicted from different reference pictures;
• signaling said sender information regarding lost pictures and a one of said plurality of representations received by said client;
• and
• sending said client a SP-picture which is the next picture in said one of plurality of representations received by client.

A method of reconstructing blocks of encoded data comprising the steps of:

• forming a prediction P(x,y) of a current block using a plurality of received motion vectors and a reference frame;
• performing a forward transform on P(x,y) to obtain a set of transform coefficients c.sub.pred for P(x,y);
• quantizing said set of transform coefficients c.sub.pred, resulting in quantized prediction image coefficients I.sub.pred.
• adding said received quantized coefficients for the prediction error I.sub.err to I.sub.pred resulting in quantized reconstruction image coefficients I.sub.rec using:
• I.sub.rec=I.sub.pred+(beta(QP2)×I.sub.err+0.5×beta(QP1))//beta(QP1).
• wherein beta(QP) is a parameter dependent on method of quantization and used OP value;
• dequantizing I.sub.rec resulting in dequantized coefficients d.sub.rec;
• and
• performing inverse transform for d.sub.rec.