Scalable lossless audio codec and authoring tool
View Patent ↗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.
1. A method of authoring an audio bitstream onto a media, comprising:
a) determining a scheme for laying out the encoded audio data from a bitstream onto a media for a decoder buffer, said bitstream including losslessly encoded most significant bit and least significant bit portions in a sequence of analysis windows;
b) calculating a buffered payload for the encoded audio data for the next analysis window;
c) if the buffered payload is within an allowed payload for an analysis window, packing the losslessly encoded most significant bit and least significant bit portions into a modified bitstream;
d) if the buffered payload exceeds the allowed payload for an analysis window,
packing the losslessly encoded most significant bit portion into the modified bitstream;
scaling the losslessly encoded least significant bit portion to a lossy encoded least significant bit portion so that the buffered payload is within the allowed payload; and
packing the lossy encoded least significant bit portion into the modified bitstream with its scaling information; and
e) repeating steps b through d for each analysis window.
2. The method of claim 1 , wherein the least significant bit portions are scaled by,
calculating a least significant bit width reduction for the analysis window;
decoding the least significant bit portions in the non-conforming windows;
reducing the least significant bit portions by the least significant bit width reduction by discarding that number of least significant bits;
encoding the modified least significant bit portions with the lossless encoding algorithm;
packing the encoded least significant bit portions; and
packing the modified least significant bit widths and the least significant bit width reduction into the bitstream.
3. The method of claim 2 , wherein the lossless encoding and decoding is simple bit replication, wherein the least significant bit portions are reduced by,
adding dither to each least significant bit portion so as to dither the next least significant bit past the least significant bit width reduction; and
shifting the least significant bit portion to the right by the least significant bit width reduction.