Coding and decoding scale factor information
Techniques and tools for representing, coding, and decoding scale factor information are described herein. For example, during encoding of scale factors, an encoder uses one or more of flexible scale factor resolution selection, spatial prediction of scale factors, flexible prediction of scale factors, smoothing of noisy scale factor amplitudes, reordering of scale factor prediction residuals, and prediction of scale factor prediction residuals. Or, during decoding, a decoder uses one or more of flexible scale factor resolution selection, spatial prediction of scale factors, flexible prediction of scale factors, reordering of scale factor prediction residuals, and prediction of scale factor prediction residuals.
1. A computer-implemented method performed by a decoder, the method comprising:
with the decoder:
parsing, from a bit stream, information indicating a selected scale factor prediction mode, wherein the selected scale factor prediction mode is selected from plural scale factor prediction modes, wherein each of the plural scale factor prediction modes is available for processing a particular mask;
performing scale factor prediction according to the selected scale factor prediction mode;
entropy decoding difference values;
combining the difference values with results of the scale factor prediction to produce plural current scale factors;
reconstructing media using the plural current scale factors; and
outputting the reconstructed media.
2. The method of claim 1 wherein the selecting occurs on a mask-by-mask basis.
3. The method of claim 1 wherein the plural scale factor prediction modes include two or more of a temporal scale factor prediction mode, a spectral scale factor prediction mode, a spatial or other cross-channel scale factor prediction mode, and a cross-layer scale factor prediction mode.
4. The method of claim 1 wherein each of the plural scale factor prediction modes predicts the plural current scale factor from a prediction, and wherein the prediction is plural previous scale factors.
5. The method of claim 1 wherein the particular mask is for a sub-frame.
6. The method of claim 1 wherein the selected scale factor prediction mode is a temporal scale factor prediction mode or a spatial scale factor prediction mode, the method further comprising performing second scale factor prediction according to a spectral scale factor prediction mode.
7. The method of claim 1 wherein the selected scale factor prediction mode is a spectral scale factor prediction mode, the method further comprising reordering difference values after entropy decoding.
8. The method of claim 1 wherein the selected scale factor prediction mode is a cross-channel scale factor prediction mode, and wherein the scale factor prediction includes predicting the plural current scale factors from plural previous scale factors from another channel.
9. A computer-implemented method performed by a decoder, the method comprising:
with the decoder:
parsing, from a bit stream, information indicating a spectral resolution for scale factors;
selecting a scale factor spectral resolution from plural scale factor spectral resolutions, wherein the selecting is based at least in part upon the parsed information, wherein the plural scale factor spectral resolutions include six different pre-defined resolutions, wherein one of the six different pre-defined resolutions is a critical band resolution and the remaining five different pre-defined resolutions are sub-critical band resolutions, and wherein the information indicating the spectral resolution indicates one of the six different pre-defined resolutions;
processing spectral coefficients with scale factors at the selected scale factor spectral resolution; and
outputting reconstructed audio samples.
10. The method of claim 9 wherein the plural scale factor spectral resolutions further include a super-critical band resolution.
11. The method of claim 9 wherein the selecting occurs for a frame that includes the spectral coefficients.
12. A computer-implemented method performed by a decoder, the method comprising:
with the decoder:
parsing, from a bit stream, information indicating a spectral resolution for scale factors;
selecting a scale factor spectral resolution from plural scale factor spectral resolutions, wherein the selecting is based at least in part upon the parsed information, wherein each of the plural scale factor spectral resolutions is available for processing a particular sub-frame of spectral coefficients, wherein the plural scale factor spectral resolutions include six different pre-defined resolutions, wherein one of the six different pre-defined resolutions is a critical band resolution and the remaining five different pre-defined resolutions are sub-critical band resolutions, and wherein the information indicating the spectral resolution indicates one of the six different pre-defined resolutions;
processing spectral coefficients including the particular sub-frame of spectral coefficients with scale factors at the selected scale factor spectral resolution; and
outputting reconstructed audio samples.
13. The method of claim 12 wherein the processing includes inverse weighting according to the scale factors.
14. The method of claim 12 wherein the selecting occurs on a frame-by-frame basis.
15. A computer-implemented method performed by an encoder, the method comprising:
with the encoder:
selecting a scale factor prediction mode from plural scale factor prediction modes, wherein each of the plural scale factor prediction modes is available for processing a particular mask;
performing scale factor prediction according to the selected scale factor prediction mode;
signaling, in a bit stream, information indicating the selected scale factor prediction mode;
computing difference values between plural scale factors for the particular mask and results of the scale factor prediction;
entropy coding the difference values; and
signaling, in the bit stream, the entropy coded difference values.
16. The method of claim 15 wherein the selecting occurs on a mask-by-mask basis.
17. The method of claim 15 wherein the plural scale factor prediction modes include two or more of a temporal scale factor prediction mode, a spectral scale factor prediction mode, a spatial or other cross-channel scale factor prediction mode, and a cross-layer scale factor prediction mode.
18. The method of claim 15 wherein each of the plural scale factor prediction modes predicts a current scale factor of the plural scale factors of the particular mask from a prediction, and wherein the prediction is a previous scale factor of a previous mask.
19. The method of claim 15 wherein the particular mask is for a sub-frame, and wherein the encoder performs the selecting based at least in part upon position of the sub-frame in a frame of multi-channel audio.
20. The method of claim 15 wherein the selected scale factor prediction mode is a temporal scale factor prediction mode or a spatial scale factor prediction mode, the method further comprising performing second scale factor prediction according to a spectral scale factor prediction mode.
21. The method of claim 15 wherein the selected scale factor prediction mode is a spectral scale factor prediction mode, the method further comprising reordering difference values prior to entropy coding.
22. The method of claim 15 wherein the selected scale factor prediction mode is a cross-channel scale factor prediction mode, and wherein the scale factor prediction includes predicting a current scale factor the plural scale factors of the particular mask from a previous scale factor of another mask from another channel.
23. A computer-implemented method performed by an encoder, the method comprising:
with the encoder:
selecting a scale factor spectral resolution from plural scale factor spectral resolutions, wherein the plural scale factor spectral resolutions include six different pre-defined resolutions, wherein one of the six different pre-defined resolutions is a critical band resolution and the remaining five different pre-defined resolutions are sub-critical band resolutions;
processing spectral coefficients with scale factors at the selected scale factor spectral resolution; and
signaling, in a bit stream, information indicating the selected scale factor spectral resolution, wherein the selected scale factor spectral resolution is one of the six different pre- defined resolutions.
24. The method of claim 23 wherein the selecting occurs for a frame that includes the spectral coefficients.
25. A computer-implemented method performed by an encoder, the method comprising:
with the encoder:
selecting a scale factor spectral resolution from plural scale factor spectral resolutions, wherein each of the plural scale factor spectral resolutions is available for processing a particular sub-frame of spectral coefficients, wherein the encoder performs the selecting based at least in part on criteria including one or more of bit rate and quality, wherein the plural scale factor spectral resolutions include six different pre-defined resolutions, wherein one of the six different pre-defined resolutions is a critical band resolution and the remaining five different pre-defined resolutions are sub-critical band resolutions;
processing spectral coefficients including the particular sub-frame of spectral coefficients with scale factors at the selected scale factor spectral resolution, wherein the processing includes weighting according to the scale factors; and
signaling, in a bit stream, information indicating the selected scale factor resolution, wherein the selected scale factor spectral resolution is one of the six different pre-defined resolutions.
26. The method of claim 25 wherein the selecting occurs on a frame-by-frame basis.