Method and apparatus for watermarking an ac-3 encoded bit stream
AssigneeThomson Licensing
InventorsXiaoming CHEN, Peter Georg Baum, Michael Arnold, Ulrich Gries
Life of this patent
Estimating the term…
Abstract
For watermark embedding, without full Dolby AC-3 decoding, mantissa bits in the AC-3 bit stream are changed by exploiting the fact that during AC-3 encoding more bits than required by the perceptual masking curve are used for the quantization of the MDCT coefficient mantissa values. In addition to the bap values, truly required bap values are determined and the mantissa values are changed accordingly, controlled by the watermark information. The advantages are efficient watermark embedding, other bit stream parameters and values remain unchanged except for CRC checks, and the audio quality of the watermarked signal remains perceptually unchanged.
Claims12
A method for watermarking an AC-3 encoded bit stream, said method comprising:
- partially decoding said AC-3 encoded bit stream, thereby providing original quantized mantissa values and exponent values derived from MDCT transform coefficients and bap values for said mantissa values, and determining the corresponding PSD values from said exponent values and determining from said PSD values the resulting masking curve;
- determining from said masking curve and said PSD values truly required bap values denoted as bap_t values;
- determining from said original mantissa values, said bap values and said bap_t values a maximum allowable mantissa value modification for a current mantissa and, if applicable, limiting a desired value for said current mantissa by said maximum allowable mantissa value modification, wherein said desired mantissa value is received from a watermarking processing;
- changing the original AC-3 mantissa bits for a current mantissa value according to said limited desired mantissa value.
An apparatus for watermarking an AC-3 encoded bit stream, said apparatus comprising:
- partial decoding means for partially decoding said AC-3 encoded bit stream, thereby providing original quantized mantissa values and exponent values derived from MDCT transform, coefficients and bap values for said mantissa values, and for determining the corresponding PSD values from said exponent values and for determining from said PSD values the resulting masking curve;
- first determining means for determining from said masking curve and said PSD values truly required bap values denoted as bap_t values;
- second determining means for determining from said original mantissa values, said bap values and said bap_t values a maximum allowable mantissa value modification for a current mantissa and, if applicable, for limiting a desired value for said current mantissa by said maximum allowable mantissa value modification, wherein said desired mantissa value is received from a watermarking processing;
- changing means for changing the original AC-3 mantissa bits for a current mantissa value according to said limited desired mantissa value.
Dependencies are inferred from the claim text.