Scalable lossless audio codec and authoring tool

Abstract

An audio codec losslessly encodes audio data into a sequence of analysis windows in a scalable bitstream. This is suitably done by separating the audio data into MSB and LSB portions and encoding each with a different lossless algorithm. An authoring tool compares the buffered payload to an allowed payload for each window and selectively scales the losslessly encoded audio data, suitably the LSB portion, in the non-conforming windows to reduce the encoded payload, hence buffered payload. This approach satisfies the media bit rate and buffer capacity constraints without having to filter the original audio data, reencode or otherwise disrupt the lossless bitstream.

18 . A method of encoding a scalable, lossless bitstream for audio data, comprising:
 determining a breakpoint that separates audio data into an MSB and an LSB portion for an analysis window;   losslessly encoding the MSB portions;   losslessly encoding the LSB portions;   packing the encoded MSB portions and LSB portions into a lossless bitstream; and   packing the bit widths of the LSB portions into the lossless bitstream.   
   
   
       19 . The method of  claim 18 , wherein the breakpoint is determined by;
 Assigning a minimum MSB bit width (Min MSB);   Computing a cost function for the audio data in the analysis window;   If the cost function exceeds a threshold, computing an LSB bit width of at least one bit that satisfies the MIN and MSB; and   If the cost function does not exceed the threshold, assigning the LSB bit width to be zero bits.   
   
   
       20 . The method of  claim 18 , wherein the LSB portions are encoded with a lossless algorithm that replicates the bits of the audio data. 
   
   
       36 . The method of  claim 18 , wherein an LSB bit width and the encoded MSB and LSB portions are packed into a bitstream for each analysis window. 
   
   
       37 . The method of  claim 18 , wherein the MSB portion is encoded with a lossless algorithm that includes decorrelation between multiple audio channels and adaptive prediction within each audio channel. 
   
   
       38 . The method of  claim 18 , wherein the LSB portion is encoded with a lossless algorithm that uses low order prediction and entropy coding. 
   
   
       39 . The method of  claim 18 , wherein the analysis windows are frames, each frame comprising a header for storing the LSB bit widths and one or more segments, each segment comprising one or more channel sets, each channel set comprising one or more audio channels, each channel comprising one or more frequency bands, said frequency bands including encoded MSB and LSB portions. 
   
   
       40 . The method of  claim 39 , wherein the bitstream has a distinct MSB and LSB split for each frequency band in each channel set in each frame. 
   
   
       41 . The method of  claim 39 , wherein said higher frequency bands include only encoded LSB portions.