Fingerprinting multimedia contents
Disclosed is a method and arrangement for extracting a fingerprint from a multimedia signal, particularly an audio signal, which is invariant to speed changes of the audio signal. To this end, the method comprises extracting ( 12,13 ) a set of robust perceptual features from the multimedia signal, for example, the power spectrum of the audio signal. A Fourier-Mellin transform ( 15 ) converts the power spectrum into Fourier coefficients that undergo a phase change only if the audio playback speed changes. Their magnitudes or phase differences ( 16 ) constitute a speed change-invariant fingerprint. By a thresholding operation ( 19 ), the fingerprint can be represented by a compact number of bits.
1 . A method of extracting a fingerprint from a multimedia signal, comprising the steps of:
extracting ( 12 , 13 ) a set of robust perceptual features from the multimedia signal;
subjecting ( 15 ) the extracted set of features to a Fourier-Mellin transform;
converting ( 16 , 19 ) the transformed set of features into a sequence constituting the fingerprint.
2 . A method as claimed in claim 1 , wherein said converting step includes converting ( 16 ,ABS) the magnitudes of the Fourier-Mellin transform.
3 . A method as claimed in claim 1 , wherein said converting step includes converting ( 16 ,Δφ) the derivative of the phase of the Fourier-Mellin transform.
4 . A method as claimed in claim 1 , wherein the multimedia signal is an audio signal and said Fourier-Mellin transform includes a one-dimensional log mapping process being applied to the set of perceptual features.
5 . A method as claimed in claim 1 , wherein the multimedia signal is an image or video signal and said Fourier-Mellin transform includes a two-dimensional log-polar mapping process being applied to the set of perceptual features.
6 . A method as claimed in claim 1 , wherein the multimedia signal is an image or video signal and said Fourier-Mellin transform includes a two-dimensional log-log mapping process being applied to the set of perceptual features.
7 . A method as claimed in claim 1 , wherein said extracting step includes normalization of the set of perceptual features.
8 . An apparatus for extracting a fingerprint from a multimedia signal, comprising:
means ( 12 , 13 ) for extracting a set of robust perceptual features from the multimedia signal;
means ( 15 ) for subjecting the extracted set of features to a Fourier-Mellin transform;
means ( 16 , 19 ) for converting the transformed set of features into a sequence constituting the fingerprint.