Methods and apparatus for embedding codes in compressed audio data streams
View Patent ↗Example methods disclosed herein to embed a watermark in a compressed audio stream include accessing a first scale factor and a first set of mantissas for a first set of transform coefficients included in the compressed audio stream, the first set of transform coefficients corresponding to a first band of a compression standard. Such disclosed example methods also include quantizing a second set of transform coefficients based on a second scale factor corresponding to the first scale factor reduced by a unit of resolution to determine a second set of mantissas, the second set of transform coefficients corresponding to the first band of the compression standard and including the watermark. Such disclosed example methods further include replacing the first scale factor with the second scale factor and the first set of mantissas with the second set of mantissas to embed the watermark in the compressed audio stream.
1. A method to embed a watermark in a compressed audio stream, the method comprising:
accessing a first scale factor and a first set of mantissas for a first set of transform coefficients included in the compressed audio stream, the first set of transform coefficients corresponding to a first band of a compression standard;
quantizing, with a processor, a second set of transform coefficients based on a second scale factor corresponding to the first scale factor reduced by a unit of resolution to determine a second set of mantissas, the second set of transform coefficients corresponding to the first band of the compression standard and including the watermark;
replacing, with the processor, the first scale factor with the second scale factor and the first set of mantissas with the second set of mantissas to modify the first set of transform coefficients to embed the watermark in the compressed audio stream to produce a watermarked compressed audio stream; and
outputting the watermarked compressed audio stream for transmission.
2. A method as defined in claim 1 , wherein the compression standard is Advanced Audio Coding (AAC).
3. A method as defined in claim 1 , wherein respective ones of the first set of transform coefficients are associated with a same scale factor, the same scale factor being the first scale factor.
4. A method as defined in claim 1 , wherein the first scale factor includes a first fractional multiplier part and a first exponent part.
5. A method as defined in claim 4 , wherein quantizing the second set of transform coefficients includes:
reducing the first scale factor by one to determine the second scale factor;
rounding a first result of dividing the second scale factor by a range of the first fractional multiplier part down to a nearest integer to determine a second exponent part;
performing a modulo operation on the second scale factor using the range of the first fractional multiplier part to determine a second fractional multiplier part;
using the second fractional multiplier part and the second exponent part to index respective lookup tables to determine a quantization step size; and
quantizing the second set of transform coefficients based on the quantization step size.
6. A method as defined in claim 5 , further including:
retrieving a first value from a first lookup table based on the second exponent part;
retrieving a second value from a second lookup table based on the second fractional multiplier part; and
multiplying the first value and the second value to determine the quantization step size.
7. An article of manufacture comprising machine readable instructions which, when executed, cause a machine to at least:
access a first scale factor and a first set of mantissas for a first set of transform coefficients included in a compressed audio stream, the first set of transform coefficients corresponding to a first band of a compression standard;
quantize a second set of transform coefficients based on a second scale factor corresponding to the first scale factor reduced by a unit of resolution to determine a second set of mantissas, the second set of transform coefficients corresponding to the first band of the compression standard and including the watermark; and
replace the first scale factor with the second scale factor and the first set of mantissas with the second set of mantissas to modify the first set of transform coefficients to embed a watermark in the compressed audio stream.
8. An article of manufacture as defined in claim 7 , wherein the compression standard is Advanced Audio Coding (AAC).
9. An article of manufacture as defined in claim 7 , wherein respective ones of the first set of transform coefficients are associated with a same scale factor, the same scale factor being the first scale factor.
10. An article of manufacture as defined in claim 7 , wherein the first scale factor includes a first fractional multiplier part and a first exponent part.
11. An article of manufacture as defined in claim 10 , wherein to quantize the second set of transform coefficients, the instructions, when executed, further cause the machine to:
reduce the first scale factor by one to determine the second scale factor;
round a first result of dividing the second scale factor by a range of the first fractional multiplier part down to a nearest integer to determine a second exponent part;
perform a modulo operation on the second scale factor using the range of the first fractional multiplier part to determine a second fractional multiplier part;
use the second fractional multiplier part and the second exponent part to index respective lookup tables to determine a quantization step size; and
quantize the second set of transform coefficients based on the quantization step size.
12. An article of manufacture as defined in claim 11 , wherein the instructions, when executed, further cause the machine to:
retrieve a first value from a first lookup table based on the second exponent part;
retrieve a second value from a second lookup table based on the second fractional multiplier part; and
multiply the first value and the second value to determine the quantization step size.
13. An apparatus to embed a watermark in a compressed audio stream, the apparatus comprising:
an embedding unit to:
access a first scale factor and a first set of mantissas for a first set of transform coefficients included in the compressed audio stream, the first set of transform coefficients corresponding to a first band of a compression standard;
quantize a second set of transform coefficients based on a second scale factor corresponding to the first scale factor reduced by a unit of resolution to determine a second set of mantissas, the second set of transform coefficients corresponding to the first band of the compression standard and including the watermark; and
replace the first scale factor with the second scale factor and the first set of mantissas with the second set of mantissas to modify the first set of transform coefficients to embed the watermark in the compressed audio stream to produce a watermarked compressed audio stream;
a modification unit to:
reconstruct an uncompressed audio stream based on the first set of transform coefficients; and
embed the watermark in the reconstructed audio stream to determine the second set of transform coefficients; and
a repacking unit to output the watermarked compressed audio stream for transmission.
14. An apparatus as defined in claim 13 , wherein the compression standard is Advanced Audio Coding (AAC).
15. An apparatus as defined in claim 13 , wherein respective ones of the first set of transform coefficients are associated with a same scale factor, the same scale factor being the first scale factor.
16. An apparatus as defined in claim 13 , wherein the first scale factor includes a first fractional multiplier part and a first exponent part.
17. An apparatus as defined in claim 16 , wherein to quantize the second set of transform coefficients, the embedding unit is further to:
reduce the first scale factor by one to determine the second scale factor;
round a first result of dividing the second scale factor by a range of the first fractional multiplier part down to a nearest integer to determine a second exponent part;
perform a modulo operation on the second scale factor using the range of the first fractional multiplier part to determine a second fractional multiplier part;
use the second fractional multiplier part and the second exponent part to index respective lookup tables to determine a quantization step size; and
quantize the second set of transform coefficients based on the quantization step size.
18. An apparatus as defined in claim 17 , wherein the embedding unit is further to:
retrieve a first value from a first lookup table based on the second exponent part;
retrieve a second value from a second lookup table based on the second fractional multiplier part; and
multiply the first value and the second value to determine the quantization step size.