Scalable lossless audio codec and authoring tool

1. A method of encoding and authoring audio data, comprising:

losslessly encoding the audio data in a sequence of analysis windows into a scalable bitstream;

separating the audio data into most significant bit (MSB) and least significant (LSB) portions for each analysis window and encoded with different lossless algorithms 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 MSB; and

if the cost function does not exceed the threshold, assigning the LSB bit width to be zero bits;

comparing a buffered payload for the encoded audio data to an allowed payload for each window; and

scaling the losslessly encoded audio data in the non-conforming windows so that the buffered payload for the bitstream does not exceed the allowed payload, said scaling operation introducing loss into the encoded data in those windows.

2. The method of claim 1 , wherein the separating step further comprising the steps of:

Computing a max LSB bit width (Max LSB) as the bit width of the audio data minus Min MSB;

Computing an L∞ norm as the maximum absolute amplitude of the audio data in the analysis window;

Computing Max Amp as the number of bits needed to represent a sample with value equal to −L∞;

Computing a squared L2 norm as the sum of the squared amplitudes of the audio data in the analysis window;

If Max Amp does not exceed Min MSB and the L2 norm does not exceed a threshold, setting the LSB bit width to zero bits;

If Max Amp does not exceed Min MSB but the L2 norm does exceed the threshold, setting the LSB bit width to the Max LSB bit width divided by a scaling factor;

If Max Amp exceeds the Min MSB, setting the LSB bit width to the Max Amp minus Min MSB.

3. The method of claim 2 , wherein the LSB bit width is limited to a maximum LSB bit width (Max LSB) determined by a word width of the audio data and Min MSB.

4. A method of encoding and authoring audio data, comprising:

losslessly encoding the audio data in a sequence of analysis windows into a scalable bitstream;

separating the audio data into most significant bit (MSB) and least significant (LSB) portions for each analysis window and encoded with different lossless algorithms;

comparing a buffered payload for the encoded audio data to an allowed payload for each window; and

authoring the audio data into the scalable bitstream by:

packing the losslessly encoded MSB portions into the bitstream for all the windows;

packing the lossessly encoded LSB portions into the bitstream for the conforming windows; and

scaling the losslessly encoded LSB portions for any non-conforming windows to make them conform, said LSB portions being scaled by:

calculating an LSB bit width reduction for the analysis window;

decoding the LSB portions in the non-conforming windows;

reducing the LSB portions by the LSB bit width reduction by discarding that number of LSBs;

encoding the modified LSB portions with the lossless encoding algorithm;

packing the encoded LSB portions; and

packing the modified LSB bit widths and the LSB bit width reduction into the bitstream.

5. The method of claim 4 , wherein the LSB bit width reduction is just enough that the buffered payload does not exceed the allowed payload.

6. A method of encoding and authoring audio data, comprising:

losslessly encoding the audio data in a sequence of analysis windows into a scalable bitstream, wherein the lossless encoding is simple bit replication;

separating the audio data into most significant bit (MSB) and least significant (LSB) portions for each analysis window and encoded with different lossless algorithms;

comparing a buffered payload for the encoded audio data to an allowed payload for each window; and

authoring the audio data into the scalable bitstream by:

packing the losslessly encoded MSB portions into the bitstream for all the windows;

packing the lossessly encoded LSB portions into the bitstream for the conforming windows; and

scaling the losslessly encoded LSB portions for any non-conforming windows to make them conform, said LSB portions being scaled by:

calculating an LSB bit width reduction for the analysis window;

decoding the LSB portions in the non-conforming windows;

reducing the LSB portions by adding dither to each LSB portion so as to dither the next LSB past the LSB bit width reduction;

shifting the LSB portion to the right by the LSB bit width reduction;

encoding the modified LSB portions with the lossless encoding algorithm;

packing the encoded LSB portions; and

packing the modified LSB bit widths and the LSB bit width reduction into the bitstream.

7. A method of encoding and authoring audio data, comprising:

losslessly encoding the audio data in a sequence of analysis windows into a scalable bitstream, wherein the audio data includes multiple channels;

separating the audio data into most significant bit (MSB) and least significant (LSB) portions for each analysis window and encoded with different lossless algorithms;

comparing a buffered payload for the encoded audio data to an allowed payload for each window; and

authoring the audio data into the scalable bitstream by:

packing the losslessly encoded MSB portions into the bitstream for all the windows;

packing the lossessly encoded LSB portions into the bitstream for the conforming windows; and

scaling the losslessly encoded LSB portions for any non-conforming windows to make them conform, said LSB portions being scaled by:

calculating an LSB bit width reduction for each channel window in accordance with a channel prioritization rule;

decoding the LSB portions in the non-conforming windows;

reducing the LSB portions by the LSB bit width reduction by discarding that number of LSBs;

encoding the modified LSB portions with the lossless encoding algorithm;

packing the encoded LSB portions; and

packing the modified LSB bit widths and the LSB bit width reduction into the bitstream.