Audio visual signature, method of deriving a signature, and method of comparing audio-visual data background

1. A method of deriving in a processor a signature characteristic of a plurality of audio samples comprising steps of:

determining audio signature data representative of the audio samples;

determining a section of the audio signature data forming a region of interest; and

providing the audio signature data section forming a region of interest as an audio signature;

wherein the step of determining audio signature data representative of the audio samples comprises the steps of:

isolating a frequency domain range of interest from the audio samples by passing the audio samples through a low-pass filter and sub-sampling the filtered audio samples; and

determining audio signature data based on a time-domain variation of the magnitude of the isolated frequency domain range of interest by comparison of each audio sample or filtered audio sample with the preceding respective audio sample or filtered audio sample to derive audio signature data in the form of a characteristic binary signal; and

where the step of determining a section of the audio signature data forming a region of interest includes the step of determining a section of the audio signature data with the greatest entropy as the region of interest.

2. The method of deriving a signature characteristic of a plurality of audio samples according to claim 1 where the provided audio signature also includes position data identifying the position of the region of interest within the audio signature data.

3. The method of deriving a signature as in claim 1 , wherein audio sample values are rectified so as to obtain absolute magnitude values.

4. A method of deriving in a processor a signature characteristic of a plurality of audio samples comprising steps of:

determining audio signature data representative of the audio samples;

determining a section of the audio signature data forming a region of interest; and,

providing the audio signature data section forming a region of interest as an audio signature, where the step of determining a section of the audio signature data forming a region of interest includes the step of determining a section of the audio signature data with the greatest entropy as the region of interest; and wherein the step of determining audio signature data representative of the audio samples comprises the steps of:

isolating a frequency domain range of interest from the audio samples by passing the audio samples through a low-pass filter and sub-sampling the filtered audio samples; and

determining audio signature data based on a time-domain variation of the magnitude of the isolated frequency domain range of interest by comparison of each audio sample or filtered audio sample with the preceding respective audio sample or filtered audio sample to derive audio signature data in the form of a characteristic binary signal.

5. The method of deriving a signature characteristic of a plurality of audio samples according to claim 4 where the provided audio signature also includes position data identifying the position of the region of interest within the audio signature data.

6. The method of deriving a signature as claimed in claim 4 where the step of determining a section of the audio signature data forming a region of interest is biased towards the selection of a section in the middle of the audio signature data.

7. A method of deriving an audio signature from two channels of audio data according to claim 4 where the said two channels are derived by the combination of two or more audio channels taken from surround-sound audio data representative of more than two channels of audio.

8. The method of deriving a signature according to claim 4 where meta-data descriptive of transient disturbances represented by the said audio data is included in the said audio signature.

9. The method of deriving a signature as claimed claim 4 , further comprising:

determining spatial profile data of video fields or frames associated with said audio samples dependent on picture information values in the video fields or frames; forming a video signature from the spatial profile data; and providing the audio signature and the video signature as an audiovisual signature.

10. The method of deriving a signature as claimed in claim 9 where the spatial profile data is obtained from averaging picture information values of a plurality of portions of the video field or frame.

11. The method of deriving a signature as claimed in claim 9 also comprising the step of determining motion profile data of video fields or frames dependent on the difference between picture information values in successive video fields or frames; wherein the video signature is formed from the spatial profile data and from motion profile data.

12. The method of deriving a signature as claimed in claim 11 where the motion profile data for a video field or frame is determined by evaluating one or more differences between spatially accumulated picture information values derived from successive video fields or frames.