# Patent

## Title
Method and apparatus for providing signatures of audio/video signals and for making use thereof

## Abstract

A method and apparatus are disclosed for providing a video signature representative of a content of a video signal. A method and apparatus are further disclosed for providing an audio signature representative of a content of an audio signal. A method and apparatus for detecting lip sync are further disclosed and take advantage of the method and apparatus disclosed for providing a video signature and an audio signature.

## Background
FIELD OF THE INVENTION
The invention relates to the processing of audio and video signals. More precisely, this invention pertains to a method and apparatus for providing signatures of audio/video signals and to a method and apparatus for using the provided signatures for detecting lip sync.
BACKGROUND OF THE INVENTION
Being able to detect differences in signals is of great interest for the skilled addressee. In the case of audio/video signals, differences may occur due to various reasons.
For instance, an audio signal may become desynchronized with a corresponding video signal during the course of a transmission of the audio/video signal. Such phenomenon is known by the skilled addressee as lip sync. Detecting lip sync may be of great interest for multiple system operators (MSO) that are looking for example to improve the quality of their channels and to avoid a phenomenon unacceptable at a certain degree for the end user.
Unfortunately, many prior art references for detecting lip sync disclose techniques that are either cumbersome to implement or require excessive processing resources.
Of interest though is PCT application WO 2008/066930 which discloses extracting features of audio and video signal content to provide reliable identification of the signals. In this international application a plurality of intermediate values are extracted. Those intermediate values represent one or more measures of dissimilarities between first and second values. Signatures are then generated by applying a hashing function on those intermediates values.
Unfortunately, the processing associated with such signature generation requires extensive processing capabilities which may not be acceptable in the case of certain applications wherein fast processing and limited processing capabilities are required.
There is therefore a need for a method and apparatus that will overcome at least one of the above-identified drawbacks.
Features of the invention will be apparent from review of the disclosure, drawings and description of the invention below.
BRIEF SUMMARY
It is an object of the invention to provide a method and apparatus for generating a video signature representative of a content of a video signal.
The content of a video signal should be understood as an indication of an evolution of the content of the video signal over time.
Yet another object of the invention is to provide a method and apparatus for generating a signature representative of a content of an audio signal.
Similarly, the content of an audio signal should be understood as an indication of an evolution of the content of the audio signal over time.
The invention provides a method for generating a video signature representative of a content of a video signal, the method comprising receiving pixel data of each of a plurality of given pixels in a first image of the video signal, receiving pixel data of each of the plurality of given pixels in a second image subsequent to the first image, for each given pixel of the plurality of given pixels, comparing corresponding pixel data of the given pixel of the first image with the corresponding pixel data of the given pixel in the second image to provide a corresponding indication of a difference between the pixel data of the given pixel of the first image and the pixel data of the given pixel in the second image; if the difference is greater than a threshold, incrementing a counter and providing an indication of the counter to thereby generate the video signature.
An advantage of the method disclosed is that such method may be used for providing information, i.e. a signature, for characterizing the content of the video signal. When signatures are used for characterizing each of two video signals, those signatures may be advantageously correlated and in turn be used for detecting a delay between the two video signals which is of great advantage.
Another advantage of the method disclosed is that it requires limited processing for generating the signature which is therefore of great advantages.
In accordance with an embodiment, the method further comprises selecting a plurality of given pixels according to at least one criteria.
In accordance with an embodiment, the at least one criteria comprises a spatial criteria.
In yet another embodiment the threshold is equal to thirty two (32).
In another embodiment of the method, the providing of the indication of the counter comprises normalizing the indication of the counter.
The invention further provides a method for generating an audio signature representative of a content of an audio signal, the method comprising receiving an audio signal; performing a first filtering of the audio signal to provide a first filtered audio signal; performing a second filtering of the audio signal to provide a second filtered audio signal; comparing the first filtered audio signal to the second filtered audio signal and assigning a value depending on the comparison to thereby generate the audio signature representative of the content of the audio signal.
An advantage of the method disclosed is that such method may be used for providing information, i.e. a signature, for characterizing the content of the audio signal. When signatures are used for characterizing each of two audio signals, those two signatures may be advantageously correlated and in turn be used for detecting a delay between the two audio signals which is of great advantage.
Other advantages of the method disclosed above are that the method requires limited processing resources and limited storing capabilities for generating the signature which is of great advantage over the prior art.
An advantage of the method disclosed is that such method may be used for detecting lip sync between a first audio/video signal and a second audio/video signal. By computing a first delay between the first audio signal and the second audio signal and a second delay between the first video signal and the second video signal and comparing the first and second delays it is possible to obtain an indication of the lip sync, if applicable.
In one embodiment of the method, the first filtering comprises detecting an envelope signal of the received audio signal.
In yet another embodiment of the method, the second filtering comprises computing an average value of the received audio signal.
In yet another embodiment, the assigning of a value depending on the comparison to thereby generate the audio signature representative of the content of the audio signal comprises performing decimation.
There is further disclosed an audio signature extraction unit for providing an audio signature signal ASi representative of a content of an audio signal Ai, the audio signature extraction unit comprising a first filtering unit for receiving the audio signal Ai and for providing a first filtered signal; a second filtering unit for receiving the audio signal Ai and providing a second filtered signal; a comparator for receiving the first filtered signal and the second filtered signal and for performing a comparison of the first filtered with the second filtered signal and for providing a comparison result to thereby provide the audio signature signal ASi representative of a content of an audio signal.
In one embodiment of the audio signature extraction unit, the first filtering unit comprises an envelope detector for providing a signal Es indicative of an envelope of the audio signal Ai.
In another embodiment of the audio signature extraction unit, the second filtering unit comprises a mean detector for providing a signal Ms indicative of a mean the audio signal Ai.
In yet another embodiment of the audio signature extraction unit, the audio signature extraction unit further comprises an absolute value providing unit for receiving the audio signal Ai and for providing a signal indicative of an absolute value of the value of the audio signal Ai; wherein each of the mean detector and the envelope detector receives the signal indicative of an absolute value of the value of the audio signal Ai.
In yet another embodiment of the audio signature extraction unit, the audio signature extraction unit further comprises a decimator for receiving the audio signature signal ASi and for decimating the audio signature signal ASi.
There is further disclosed a video signature extraction unit for providing a video signature signal VSi representative of a content of an incoming image signal Vi, the video signature extraction unit comprising a first image pixel data providing unit for receiving the incoming image signal Vi and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image; a second image pixel data providing unit for receiving the incoming image signal Vi and for providing a corresponding pixel data Ck of the corresponding given pixel k in a second image; a comparator for receiving the corresponding pixel data Pk and the corresponding pixel data Ck and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck to provide an a result signal indicative of the comparison; a counter for receiving and counting the result signal of each of the plurality of given pixels 1 to N and for providing a counter signal and a video signature providing unit for receiving the counter signal and for providing the video signature signal VSi.
In one embodiment of the video signature extraction unit, the result signal is a logic value one (1) if Abs(Pk−Ck) is greater than thirty two (32) and a logic value zero (0) otherwise.
In yet another embodiment of the video signature extraction unit, the video signature providing unit receives the counter signal and divides the counter signal by N/15, wherein N is the number of given pixels.
In yet another embodiment of the video signature extraction unit, the video signature extraction unit further comprises a windowing unit for receiving the incoming image signal Vi and for providing a selected signal Wi.
There is further provided an apparatus for providing an indication of a lip sync, the apparatus comprising a first audio signature extraction unit for receiving a first audio signal and a first video signal and for providing a first video signature and a first audio signature; a second signature extraction unit for receiving a second audio signal and a second video signal and for providing a second video signature and a second audio signature and a signature analysis unit for receiving the first video signature, the first audio signature, the second video signature and the second audio signature and for correlating the first video signature with the second video signature to provide a video delay and for further correlating the first audio signature with the second audio signature to provide an audio delay, the signature analysis unit for further comparing the audio delay with said video delay and for providing an indication of a lip sync is the audio delay is different from said video delay.
In one embodiment of the apparatus for providing an indication of a lip sync, the first signature extraction unit comprises a first audio signature extraction unit for receiving the first audio signal and for providing the first audio signature signal and the first signature extraction unit comprises a first video signature extraction unit for receiving the first video signal and for providing the first video signature signal.
In yet another embodiment of the apparatus for providing an indication of a lip sync, the second signature extraction unit comprises a second audio signature extraction unit for receiving the second audio signal and for providing the second audio signature signal and the second signature extraction unit comprises a second video signature unit for receiving the second video signal and for providing the second video signature signal.
In yet another embodiment of the apparatus for providing an indication of a lip sync, the first audio signature extraction unit comprises a first filtering unit for receiving the first audio signal and for providing a first filtered signal, a second filtering unit for receiving the first audio signal and for providing a second filtered signal, a comparator for receiving the first filtered signal and the second filtered signal and for performing a comparison of the first filtered with the second filtered signal and for providing a comparison result to thereby provide the first audio signature signal.
In yet another embodiment of the apparatus for providing an indication of a lip sync, the first video signature extraction unit comprises a first image pixel data providing unit for receiving the first video signal and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image of the first video signal; a second image pixel data providing unit for receiving the first video signal and for providing a corresponding pixel data Ck of the corresponding given pixel k in a second image of the first video signal; a comparator for receiving the corresponding pixel data Pk and the corresponding pixel data Ck and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck to provide a result signal indicative of the comparison; a counter for receiving and counting the result signal of each of the plurality of given pixels 1 to N and for providing a counter signal; and a video signature providing unit for receiving the counter signal and for providing the first video signature signal.
In yet another embodiment of the apparatus for providing an indication of a lip sync, the second audio signature extraction unit comprises a first filtering unit for receiving the second audio signal and for providing a first filtered signal; a second filtering unit for receiving the second audio signal and for providing a second filtered signal; a comparator for receiving the first filtered signal and the second filtered signal and for performing a comparison of the first filtered with the second filtered signal and for providing a comparison result to thereby provide the second audio signature signal.
In yet another embodiment of the apparatus for providing an indication of a lip sync, the second video signature extraction unit comprises a first image pixel data providing unit for receiving the second video signal and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image of the second video signal; a second image pixel data providing unit for receiving the second video signal and for providing a corresponding pixel data Ck of the corresponding given pixel k in a second image of the second video signal; a comparator for receiving the corresponding pixel data Pk and the corresponding pixel data Ck and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck to provide a result signal indicative of the comparison; a counter for receiving and counting the result signal of each of the plurality of given pixels 1 to N and for providing a counter signal and a video signature providing unit for receiving the counter signal and for providing the second video signature signal.
Another advantage of the embodiment disclosed is that it may be used for content comparison instead of lip sync detection.
Alternatively, the embodiment disclosed may be used for detecting pirated copies or for checking that a given ads has been properly inserted in a video signal. This may be done by comparing the video signal carrying the ads and the ads per se.



BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be readily understood, embodiments of the invention are illustrated by way of example in the accompanying drawings.
FIG. 1 is a flowchart which shows an embodiment of a method for generating a signature representative of a content of a video signal;
FIG. 2 is a flowchart which shows an embodiment of a method for generating a signature representative of a content of an audio signal;
FIG. 3A is a block diagram which shows an embodiment of an apparatus for generating a video signature representative of a content of a video signal;
FIG. 3B is a schematic which shows how the video signature representative of a content of a video signal is generated according to one embodiment;
FIG. 3C is a block diagram which shows an embodiment of a video signature extraction unit;
FIG. 4A is a block diagram which shows an embodiment of an apparatus for generating an audio signature representative of a content of an audio signal;
FIG. 4B is a block diagram which shows an embodiment of an apparatus for generating an audio signature representative of a content of an audio signal; in this embodiment, the apparatus for generating an audio signature representative of a content of an audio signal comprises, inter alia, an envelope detector, a mean detector and a comparator;
FIG. 5 is a block diagram of an embodiment of an apparatus comprising an audio signal signature extraction unit, a video signal signature extraction unit and a signature analysis unit for providing, inter alia, an indication of a lip sync;
FIG. 6 is a block diagram which shows an embodiment of the signature analysis unit disclosed in FIG. 5;
FIG. 7A is a schematic which shows an embodiment of two streams of video signature signals delayed in time;
FIG. 7B is a block diagram which shows an embodiment of a video signature analysis unit used for analyzing two video signature signals;
FIG. 7C is a graph which shows an embodiment of a variation of the result of the convolution of a first video signature signal with a second video signature signal;
FIG. 8A is a schematic which shows an embodiment of two streams of audio signature signals delayed in time;
FIG. 8B is a block diagram which shows an embodiment of an audio signature analysis unit used for analyzing two audio signature signals; and
FIG. 8C is a graph which shows an embodiment of a variation of the result of the convolution of a first audio signature signal with a second audio signature signal.



Further details of the invention and its advantages will be apparent from the detailed description included below.
DETAILED DESCRIPTION
In the following description of the embodiments, references to the accompanying drawings are by way of illustration of an example by which the invention may be practiced. It will be understood that other embodiments may be made without departing from the scope of the invention disclosed.
Now referring to FIG. 1, there is shown an embodiment of a method for generating a video signature representative of a content of a video signal. It will be appreciated that generating a video signature representative of a content of a video signal may be of great advantage for various reasons as further explained herein below.
According to processing step 102, pixel data of each of a plurality of given pixels in a first image are received.
It will be appreciated that in one embodiment, the image originates from a digital video stream. Alternatively, the image may originate from an analog video stream. In other embodiments, the image may originate from a file-based source.
The skilled addressee will appreciate that the given pixels are pixels that may be selected in the image according to various criteria. For instance, the given pixels may be selected according to spatial criteria. For instance, it has been contemplated that some parts of an image may be of less interest for the purpose of generating a signature.
This may be the case for instance for parts of an image where no significant changes occur. Alternatively, it may be the case for parts of an image resulting from a format conversion. Alternatively, those parts of an image may be parts of images that have been modified for branding reasons.
In one embodiment a windowing may be accordingly performed on a part of interest of an image in order to remove those parts of the image that have a limited interest.
In a preferred embodiment, the given pixels are pixels each separated from one another by a given amount of pixels. The amount of given pixels does not change when the resolution of the video signal changes in the preferred embodiment. Alternatively, the amount of given pixels changes when the resolution of the video signal changes.
According to processing step 104, pixel data of each of a plurality of given pixels in a second image are received.
It will be appreciated that the second image is an image following in time the first image in the video signal.
In a preferred embodiment, the second image is immediately following the first image in the video signal.
According to processing step 106, a comparison is performed.
In one embodiment, the comparison is performed for each given pixel of the plurality of given pixels.
More precisely, corresponding pixel data of the given pixel of the first image is compared with the corresponding pixel data of the given pixel in the second image in order to provide a corresponding indication of a difference between the pixel data of the given pixels of the first image and the pixel data of the given pixel in the second image.
In one embodiment, the comparison is a subtraction of the pixel data of the given pixel of the first image with corresponding pixel data of the given pixel of the second image. The comparison is performed for each given pixel of the plurality of given pixels.
Alternatively the comparison may be a combination of operations involving the pixel data of each of the given pixels of the first image with corresponding pixel data of each of the given pixels of the second image.
According to processing step 108, a counter value is incremented based on the result of the comparison.
In one embodiment, the counter value is incremented in the case where the result of the operation is greater than a given threshold value.
The skilled addressee will appreciate that various embodiments of the given threshold value may be provided. In a preferred embodiment, the threshold value is equal to thirty two (32) on an 8 bit precision video pixel.
Moreover, it will be appreciated that the given threshold value may be provided according to various criteria such as a type of video signal.
According to processing step 110, an indication of the counter value is provided. The indication of the counter value is used as the video signature representative of a content of the video signal.
It will be appreciated that in one embodiment, the processing step of providing the indication of a counter value may comprise normalizing the counter value to provide a counter value limited by a given value.
In a preferred embodiment, a normalizing of the counter value is performed by dividing the counter value by (N/15) where N is the number of given pixels.
The skilled addressee will appreciate that the method disclosed for providing a video signature representative of a content of the video signal is of great advantage for various reasons.
An advantage of the method disclosed is that such method may be used for providing information, i.e. a signature, for characterizing the content of the video signal. When signatures are used for characterizing each of two video signals, those signatures may be advantageously correlated and in turn be used for detecting a delay between the two video signals which is of great advantage.
Another advantage of the method disclosed is that it requires limited processing resources for generating the signature which is therefore of great advantages. Such method does not require any complex algorithm for analyzing the content of the video signal.
Another advantage of the method is that its implementation requires limited storing resources.
Now referring to FIG. 2, there is shown an embodiment of a method for generating an audio signature representative of a content of an audio signal. It will be appreciated that generating an audio signature representative of a content of an audio signal may be of great advantage for various reasons as further explained below.
According to processing step 202, an audio signal is received. It will be appreciated that the audio signal may be received from various sources. For instance, the audio signal may be receiving from an audio stream. Alternatively, the audio signal may be received from a file. It will further be appreciated that the audio signal may be imbedded in a video stream.
Moreover, it will be appreciated that the audio signal may be provided in various forms such as in a digital format or in an analog format. Moreover it will be appreciated that the audio signal may be formatted according to various standards known to the skilled addressee.
According to processing step 204, a first filtering of the received audio signal is performed.
In one embodiment, the first filtering of the received audio signal comprises detecting an envelope of the audio signal.
According to processing step 206, a second filtering of the received audio signal is performed.
In one embodiment, the second filtering of the received audio signal comprises computing an average value of the received audio signal.
It will be appreciated by the skilled addressee that processing steps 204 and 206 may be performed in parallel. Alternatively, processing steps 204 and 206 may be performed serially.
According to processing step 208, the first filtered audio signal is compared to the second filtered audio signal.
It will be appreciated that the comparison may be a combination of operations involving the first filtered audio signal and the second filtered audio signal.
In a preferred embodiment, the comparison comprises checking if the first filtered audio signal is greater than the second filtered audio signal.
According to processing step 210, a value is assigned depending on the result of the comparison. It will be appreciated that the value may be any type of value.
In a preferred embodiment, the value is a binary value. Still in a preferred embodiment, binary value one (1) is assigned if the first filtered audio signal is greater than the second filtered audio signal while binary value zero (0) is assigned if the second filtered audio signal is greater or equal than the first filtered audio signal.
According to processing step 212, the assigned value is provided. It will be appreciated that the assigned value. The assigned value is used as the audio signature representative of a content of the audio signal.
It will be appreciated that in a preferred embodiment the providing of the assigned value may comprise a decimation processing step. The skilled addressee will appreciate that the purpose of the decimation processing step is to remove a given amount of unwanted/redundant data. The skilled addressee will also appreciate that this will further result in a signature having a shorter size which is also of great advantage.
The skilled addressee will appreciate that the method disclosed for providing an audio signature representative of a content of the audio signal is of great advantage for various reasons.
An advantage of the method disclosed is that such method may be used for providing information, i.e. a signature, for characterizing the content of the audio signal. When signatures are used for characterizing each of two audio signals, those two signatures may be advantageously correlated and in turn be used for detecting a delay between the two audio signals which is of great advantage.
Another advantage of the method disclosed above is that they require limited processing resources for generating the signature which is of great advantage.
A further advantage is that the implementation of the method disclosed may require limited memory resource which is also of great advantage.
Now referring to FIG. 3a, there is shown an embodiment of an apparatus 300 for providing a video signature.
The apparatus 300 for providing a video signature comprises an optional windowing unit 302 and a video signature extraction unit 304.
More precisely, the optional windowing unit 302 is used for performing a windowing of an incoming image signal Vi. The optional windowing unit 302 provides a corresponding selected signal Wi. The skilled addressee will appreciate that the optional windowing unit 302 may be implemented according to various embodiments known to the skilled addressee.
The apparatus 300 for providing a video signature further comprises the video signature extraction unit 304.
The video signature extraction unit 304 is used for extracting a video signature from an incoming video signal. In this embodiment, the video signature extraction unit 304 receives the selected signal Wi provided by the optional windowing unit 302 and provides a video signature signal VSi.
Now referring to FIG. 3B, there is shown an embodiment which shows how the video signature extraction unit 304 operates according to an embodiment.
In accordance with this embodiment, a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image is compared with a corresponding pixel data Ck of the corresponding given pixel k in a second image in order to provide a corresponding indication of a difference |Pk−Ck| between the pixel data of the given pixel of the first image and the pixel data of the given pixel in the second image.
An absolute value of the result, |Pk−Ck|, of the comparison is taken. In the case where the absolute value of the result is larger than a given threshold value, binary value one (1) is assigned. If this is not the case, binary value zero (0) is assigned. Such operation is performed for each pixel of the plurality of given pixels.
Moreover, an optional normalization of the result may be performed. The video signature signal may be therefore defined as:




  
    
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The skilled addressee will appreciate that various other alternative embodiments may be provided.
Now referring to FIG. 3C, there is shown an embodiment of the video signature extraction unit 304.
The video signature extraction unit 304 comprises a first image pixel data providing unit 306, a second image pixel data providing unit 308, a comparator 310, a counter 312 and a video signature providing unit 314.
The first image pixel data providing unit 306 is used for receiving the selected signal Wi provided by the optional windowing unit 302 and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of the first image.
Similarly, the second image pixel data providing unit 308 is used for receiving the selected signal Wi provided by the optional windowing unit 302 and for providing a corresponding pixel data Ck of the corresponding given pixel k in the second image.
The comparator 310 is used for receiving the corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of the first image and the corresponding pixel data Ck of the corresponding given pixel k in the second image and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck.
In one embodiment, the comparator 310 outputs a logic value one (1) if |Pk−Ck| is greater than thirty two (32) and a logic value zero (0) otherwise.
The counter 312 receives the output from the comparator 310 and provides a signal indicative of a number of logic value ones received by the counter 312.
The video signature providing unit 314 receives the signal indicative of a number of logic value ones received by the counter 312 and provides the video signature signal VSi. In one embodiment, the video signature providing unit 314 performs a division of the signal indicative of a number of logic value ones received by the counter 312 by N/15 wherein N is the number of given pixels.
Now referring to FIG. 4A, there is shown an embodiment of an apparatus 402 for generating an audio signature representative of a content of an audio signal.
In this embodiment, the apparatus 402 for generating an audio signature representative of a content of an audio signal receives an audio signal Ai and provides a corresponding audio signature signal ASi.
It will be appreciated that the audio signal Ai may be of various forms such as in a digital format or in an analog format. Moreover it will be appreciated that the audio signal may be formatted according to various standards as already explained above.
Similarly, it will be appreciated that the corresponding audio signature signal ASi may be of various forms such as in a digital format or in an analog format. Moreover it will be appreciated that the corresponding audio signature signal ASi may be formatted according to various standards as explained above.
Now referring to FIG. 4B, there is shown an embodiment of the apparatus 402 for generating an audio signature representative of a content of an audio signal.
In this embodiment, the apparatus 402 for generating an audio signature representative of a content of an audio signal comprises an absolute value providing unit 404, an envelope detector 406, a mean detector 408, a comparator 410 and a decimator 412.
The absolute value providing unit 404 is used to provide a signal indicative of an absolute value of the audio signal Ai.
The envelope detector 406 is used to provide a signal Es indicative of an envelope of the signal indicative of an absolute value of the value of the audio signal Ai. It will be appreciated that the envelope detector 406 is an embodiment of a first filtering unit.
Moreover, it will be appreciated that the envelope detector 406 may be implemented in various ways as known by the skilled addressee.
In a preferred embodiment, the envelope detector 406 is implemented using a one-tap Infinite Impulse Response (IIR) filter.
The mean detector 408 is used to provide a signal Ms indicative of a mean of the signal indicative of an absolute value of the value of the audio signal Ai. It will be appreciated that the mean detector 408 is an embodiment of a second filtering unit.
Moreover, it will be appreciated that the mean detector 408 may be implemented in various ways as known by the skilled addressee.
In a preferred embodiment, the mean detector 408 is implemented using a one-tap Infinite Impulse Response (IIR) filter.
The comparator 410 is used for making a comparison between two incoming signals. More precisely, the comparator 410 receives the signal Ms indicative of a mean of the signal indicative of an absolute value of the value of the audio signal Ai and the signal Es indicative of an envelope of the signal indicative of an absolute value of the value of the audio signal Ai and performs a comparison between those two signals.
If the signal Es indicative of an envelope of the signal indicative of an absolute value of the value of the audio signal A is greater than the signal Ms indicative of a mean of the signal indicative of an absolute value of the value of the audio signal Ai, a one (1) logic value signal is outputted by the comparator 410. Otherwise a zero (0) logic value signal is outputted by the comparator 410.
The skilled addressee will appreciate that various other types of comparison may be made.
Moreover, it will be appreciated that the comparator 410 may be implemented in various ways.
The decimator 412 is used for performing decimation on a signal provided by the comparator 410. The decimator 412 provides the audio signature signal ASi.
It will be appreciated that the decimator 412 is optional.
Moreover, it will be appreciated that the decimator 412 may be implemented in various ways as known by the skilled addressee. In one embodiment, a decimation by fifty two (52) is performed by the decimator 412.
In a preferred embodiment, the decimator 412 takes a sample and ignores fifty one (51) following samples. Alternatively, the sample is taken every one (1) ms. Other methods may alternatively be used. For instance, those methods may take into consideration the value of each sample for selecting a given sample.
Now referring to FIG. 5, there is shown an embodiment of an apparatus 500 which uses an audio signal signature extraction unit and a video signal signature extraction unit for providing, inter alia, an indication of a lip sync.
In this embodiment, a first audio/video content is to be compared to a second audio/video content.
More precisely, the first audio/video content comprises a first audio signal and a first video signal while the second audio/video content comprises a second audio signal an a second video signal.
As shown below, by carefully comparing the signatures of the first audio/video content with the signatures of the second audio/video content it is possible to provide an indication of a lip sync, i.e. to providing an indication of a desynchronization that occurred between the video signal and its corresponding audio signal. As known by the skilled addressee, such desynchronization may occur for various reasons such as for instance for reasons associated with the transmission of the signals over a medium.
More precisely and as shown in FIG. 5, the apparatus 500 comprises a first signature extraction unit 502, a second signature extraction unit 504 and a signature analysis unit 506.
The first signature extraction unit 502 is used for providing a first video signature signal VS1 and a first audio signature signal AS1 of respectively a first video signal V1 and a first audio signal A1 associated with the first video signal V1.
The first signature extraction unit 502 comprises, as not shown in FIG. 5, an audio signature extraction unit and a video signature extraction unit each responsible for respectively receiving the first audio signal A1 and providing the first audio signature signal AS1 and receiving the first video signal V1 and providing the first video signature signal VS1. Such video signature extraction unit and audio signature extraction unit have been already described above.
The second signature extraction unit 504 is used for providing a second video signature signal VS2 and a second audio signature signal AS2 of respectively a second video signal V2 and a second audio signal A2 associated with the second video signal V2.
The second signature extraction unit 504 comprises, as not shown in FIG. 5, an audio signature extraction unit and a video signature extraction unit each responsible for respectively receiving the second audio signal A2 and providing the second audio signature signal AS2 and receiving the second video signal V2 and providing the second video signature signal VS2. Such video signature extraction unit and audio signature extraction unit have also been already described above.
The signature analysis unit 506 is used for receiving the first video signature signal VS1, the first audio signature signal AS1, the second video signature signal VS2 and the second audio signature signal AS2.
The signature analysis unit 506 provides a signal VD indicative of a video delay, a signal AD indicative of an audio delay, a signal LS indicative of a lip sync, a signal VMF indicative of a video matching factor and a signal AMF indicative of an audio matching factor.
The signal VD indicative of a video delay is generated by comparing the first video signature signal VS1 with the second video signature signal VS2 and by determining a delay between those two signals as shown further below.
Similarly, the signal AD indicative of an audio delay is generated by comparing the first audio signature signal AS1 with the second audio signature signal AS2 and by determining a delay between those two signals as shown further below.
The signal VMF indicative of a video matching factor and the signal AMF indicative of an audio matching factor are generated as further explained below.
Finally and in one embodiment, the signal LS indicative of a lip sync is generated by comparing the signal VD indicative of a video delay with the signal AD indicative of an audio delay.
In the implementation described herein the signal VMF indicative of a video matching factor and the signal AMF indicative of an audio matching factor are further used for generating the signal LS indicative of a lip sync.
While the embodiment disclosed in FIG. 5 has been shown to be used for lip sync detection, the skilled addressee will appreciate that such embodiment may be advantageously used for content comparison for instance.
Alternatively, the embodiment may be used for detecting pirated copies. In an alternative embodiment, the method disclosed may be used for checking that a given ads has been properly inserted in a video signal. This may be done by comparing the signatures of the audio/video signal carrying the ads and the signatures of the ads per se.
Now referring to FIG. 6, there is shown an embodiment of the signature analysis unit 506 disclosed in FIG. 5.
The signature analysis unit 506 comprises a video signature analysis unit 602, an audio signature analysis unit 604 and a video signature correlation analysis unit 606.
The video signature analysis unit 602 is used for determining an estimation VD′ of the signal indicative of a video delay between the first video signature signal VS1 and the second video signature signal VS2.
The video signature analysis unit 602 is further used for determining an estimation VMF′ of a signal indicative of a video matching factor.
Similarly, the audio signature analysis unit 604 is used for determining an estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2.
The audio signature analysis unit 604 is further used for determining an estimation AMF′ of a signal indicative of an audio matching factor.
The video signature correlation analysis unit 606 receives the estimation VD′ of the signal indicative of a video delay between the first video signature signal VS1 and the second video signature signal VS2, the estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2, the estimation VMF′ of a signal indicative of a video matching factor and the estimation AMF′ of a signal indicative of an audio matching factor.
The video signature correlation analysis unit 606 provides the signal LS indicative of a lip sync, the signal VD indicative of a video delay, the signal AD indicative of an audio delay, the signal VMF indicative of a video matching factor and the signal AMF indicative of an audio matching factor.
In one embodiment, the signal LS indicative of a lip sync is defined as LS=(VD′−AD′) if VMF′≧threshold1& AMF′≧threshold2, wherein threshold1 and threshold2 are given values. In one embodiment, the threshold1 is equal to 50% while the threshold2 is equal to 40%. The skilled addressee will appreciate that various other values may be used.
The skilled addressee will appreciate that the signal VD indicative of a video delay and the signal AD indicative of an audio delay are generated using respectively at least the estimation VD′ of the signal indicative of a video delay between the first video signature signal VS1 and the second video signature signal VS2 and the estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2. In fact, the skilled addressee will appreciate that estimations are first computed prior to provide the values for the sake validating the values.
Now referring to FIG. 7A, there are shown a graph 702 showing an example of the first video signature signal VS1 and a graph 704 showing an example of the second video signature signal VS2.
It will be appreciated that the first video signature signal VS1 and the second video signature signal VS2 are desynchronized in time by an amount of time corresponding to the estimation VD′ of the signal indicative of a video delay between the first video signature signal VS1 and the second video signature signal VS2. Still in this embodiment, the first video signature signal VS1 is delayed in time compared to the second video signature signal VS2.
Now referring to FIG. 7B, there is shown an embodiment of the video signature analysis unit 602.
The video signature analysis unit 602 comprises a convolution unit 706 and a minimum detection and delay extraction unit 708.
The convolution unit 706 is used for performing a convolution of the first video signature signal VS1 and the second video signature signal VS2. In one embodiment the convolution is a time shifted convolution of the second video signature signal VS2 window across the first video signature signal VS1 window.
In one embodiment, the second video signature signal VS2 window has a value of twenty (20) seconds while the first video signature signal VS1 window has a value of thirty (30) seconds.
The convolution unit 706 provides a convolution signal EV(t).
It will be appreciated by the skilled addressee that the convolution may be alternatively performed in various other ways. Moreover it will be appreciated that the convolution unit 706 may implemented in various way.
The minimum detection and delay extraction unit 708 is used for detecting a minimum in the convolution signal EV(t). It will be appreciated that the minimum in the convolution signal EV(t) is indicative of the estimation VD′ of the signal indicative of a video delay between the first video signature signal VS1 and the second video signature signal VS2.
The minimum detection and delay extraction unit 708 is further used for providing the estimation VMF′ of a signal indicative of a video matching factor.
It will be appreciated that the signal VMF indicative of a video matching factor is indicative of a level of similarity measured in the video signatures.
It will be appreciated that the signal estimation VMF′ of a signal indicative of a video matching factor is a function of the convolution signal EV(t) and the estimation VD′ of the signal indicative of a video delay between the first video signature signal VS1 and the second video signature signal VS2.
In a preferred embodiment, the signal estimation VMF′ of a signal indicative of a video matching factor is defined as
VMF′=100*(1−(Min(EV(t))/Sum(VS2)), wherein VMF′ is the estimated video matching factor between the first video signature signal VS1 and the second video signature signal VS2 and is expressed in percentage, Min(EV(t)) is the minimum error found in the video correlation graph disclosed at FIG. 7c, and Sum(VS2) is the sum of the signature vector in the window V2. It will be appreciated that in that embodiment, when V1 and V2 are exactly the same, VMF′ is equal to 100% while if one of the two video sources is altered, VMF′ will be reduced. In this embodiment, under 50%, the video sources are considered to be different.
It will be appreciated that the minimum detection and delay extraction unit 708 may be implemented in various ways.
Now referring to FIG. 8, there are shown a graph 800 showing an example of the first audio signature signal AS1 and a graph 802 showing an example of the second audio signature signal AS2.
It will be appreciated that the first audio signature signal AS1 and the second audio signature signal AS2 are desynchronized in time by an amount of time corresponding to the estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2. Still in this embodiment, the first audio signature signal AS1 is delayed in time compared to the second audio signature signal AS2.
Now referring to FIG. 8B, there is shown an embodiment of audio signature analysis unit 604 for determining the estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2 and the estimation AMF′ of a signal indicative of an audio matching factor.
The audio signature analysis unit 604 comprises a convolution unit 804 and a minimum detection and delay extraction unit 806.
The convolution unit 804 is used for performing a convolution of the first audio signature signal AS1 and the second audio signature signal AS2. In one embodiment the convolution is a time shifted convolution of the second audio signature signal AS2 window across the first audio signature signal AS1 window.
In one embodiment, the second audio signature signal AS2 window has a value of one (1) second while the first audio signature signal AS1 window has a value of ten (10) seconds. It will be appreciated that those values may be changed depending on various needs.
The convolution unit 804 provides a convolution signal EA(t).
It will be appreciated by the skilled addressee that the convolution may be alternatively performed in various other ways. Moreover it will be appreciated that the convolution unit 804 may implemented in various ways.
The minimum detection and delay extraction unit 806 is used for detecting a minimum in the convolution signal EA(t). It will be appreciated that the minimum in the convolution signal EA(t) is indicative of the estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2.
The minimum detection and delay extraction unit 806 is further used for providing the signal estimation AMF′ of a signal indicative of an audio matching factor.
It will be appreciated that the signal estimation AMF′ of a signal indicative of an audio matching factor is indicative of a level of similarity measured in the audio signatures.
It will be appreciated that the signal estimation AMF′ of a signal indicative of an audio matching factor is a function of the convolution signal EA(t) and the estimation AD′ of the signal indicative of an audio delay between the first audio signature signal AS1 and the second audio signature signal AS2.
In a preferred embodiment, the signal estimation AMF′ of a signal indicative of an audio matching factor is defined as:
AMF′=100*(1−Min((EA(t))/(Size(AS2)/5)), wherein AMF′ is the estimated audio matching factor between the first audio signature signal AS1 and the second audio signature signal AS2 expressed in percentage, Min((EA(t)) is the minimum error found in the audio correlation graph shown in FIG. 8c and Size(AS2) is the size of the audio signature vector in the window WA2. It will be appreciated that when A1 and A2 are exactly the same, the signal estimation AMF′ of a signal indicative of an audio matching factor is equal to 100%. If one of the two audio sources was altered, the signal estimation AMF′ of a signal indicative of an audio matching factor will be reduced. Still in this embodiment, when the signal estimation AMF′ of a signal indicative of an audio matching factor is under 40%, the audio sources are considered to be different.
It will be appreciated that the minimum detection and delay extraction unit 806 may be implemented in various ways. For instance, the minimum detection and delay extraction unit 806 may first perform a pre-scan in order to select a first selection of convoluted samples. In one embodiment the first selection represents one-eight (1⁄8) of all the convoluted samples. A search may then be performed in the selected convoluted samples.
Although the above description relates to a specific preferred embodiment as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.

## Claims

1. A method for generating a video signature representative of a content of a video signal, the method comprising:
receiving pixel data of each of a plurality of given pixels in a first image of the video signal,
receiving pixel data of each of the plurality of given pixels in a second image subsequent to the first image,
for each given pixel of the plurality of given pixels,
comparing corresponding pixel data of the given pixel of the first image with the corresponding pixel data of the given pixel in the second image to provide a corresponding indication of a difference between the pixel data of the given pixel of the first image and the pixel data of the given pixel in the second image;
if the difference is greater than a threshold, incrementing a counter;
normalizing the indication of the counter by dividing the counter signal by a value proportional to N, wherein N is the number of given pixels; and
providing the normalized indication of the counter to thereby generate said video signature.

2. The method as claimed in claim 1, further comprising selecting a plurality of given pixels according to at least one criteria.

3. The method as claimed in claim 2, wherein the at least one criteria comprises a spatial criteria.

4. The method as claimed in claim 1, wherein the pixel data of the given pixel in the first image and the pixel data of the given pixel in the second image each comprise an 8-bit numerical value between zero (0) and two hundred and fifty five (255), and wherein the threshold comprises a difference between the numerical values of the pixel data of the given pixel of the first image and the pixel data of the given pixel of the second image that is equal to a numerical value of thirty two (32).

5. A method for generating an audio signature representative of a content of an audio signal, the method comprising:
receiving an audio signal;
performing a first filtering of the audio signal to provide a first filtered audio signal;
performing a second filtering of the audio signal to provide a second filtered audio signal;
comparing the first filtered audio signal to the second filtered audio signal; and
assigning a value depending on the comparison, and decimating a plurality of assigned values by removing N−1 of every N assigned values, wherein N is a predetermined number of values, to thereby generate the audio signature representative of the content of the audio signal.

6. The method as claimed in claim 5, wherein said first filtering comprises detecting an envelope signal of the received audio signal.

7. The method as claimed in claim 6, wherein said second filtering comprises computing an average value of the received audio signal.

8. An audio signature extraction unit for providing an audio signature signal ASi representative of a content of an audio signal Ai, the audio signature extraction unit comprising:
a first filtering unit for receiving the audio signal Ai and for providing a first filtered signal;
a second filtering unit for receiving the audio signal Ai and providing a second filtered signal;
a comparator for receiving the first filtered signal and the second filtered signal and for performing a comparison of the first filtered with the second filtered signal and for providing a comparison result to thereby provide the audio signature signal ASi representative of a content of an audio signal; and
a decimator for receiving the audio signature signal ASi and for decimating the audio signature signal ASi by removing N−1 of every N assigned values, wherein N is a predetermined number of values.

9. The audio signature extraction unit as claimed in claim 8, wherein said first filtering unit comprises an envelope detector for providing a signal Es, indicative of an envelope of the audio signal Ai.

10. The audio signature extraction unit as claimed in claim 9, wherein said second filtering unit comprises a mean detector for providing a signal Ms, indicative of a mean the audio signal Ai.

11. The audio signature extraction unit as claimed in claim 10, further comprising an absolute value providing unit for receiving the audio signal Ai and for providing a signal indicative of an absolute value of the value of the audio signal Ai; wherein each of said mean detector and said envelope detector receives said signal indicative of an absolute value of the value of the audio signal Ai.

12. A video signature extraction unit for providing a video signature signal VSi representative of a content of an incoming image signal Vi the video signature extraction unit comprising:
a first image pixel data providing unit for receiving the incoming image signal Vi and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image of the incoming image signal Vi;
a second image pixel data providing unit for receiving the incoming image signal Vi and for providing a corresponding pixel data Ck of the corresponding given pixel k in a second image of the incoming image signal Vi;
a comparator for receiving the corresponding pixel data Pk and the corresponding pixel data Ck and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck to provide a result signal indicative of the comparison;
a counter for receiving and counting the result signal of each of the plurality of given pixels 1 to N and for providing a counter signal; and
a video signature providing unit for receiving the counter signal, normalizing the counter signal by dividing the counter signal by a value proportional to N, wherein N is the number of given pixels, and for providing the video signature signal VSi.

13. The video signature extraction unit as claimed in claim 12, wherein Pk and Ck each comprise an 8-bit numerical value between zero (0) and two hundred and fifty five (255), and wherein the result signal is a logic value one (1) if |Pk−Ck| is greater than a numerical value of thirty two (32) and a logic value zero (0) otherwise.

14. The video signature extraction unit as claimed in claim 12, further comprising a windowing unit for receiving the incoming image signal Vi and for providing a selected signal Wi.

15. An apparatus for providing an indication of a lip sync, the apparatus comprising:
a first signature extraction unit for receiving a first audio signal and a first video signal and for providing a first video signature signal and a first audio signature signal;
a second signature extraction unit for receiving a second audio signal and a second video signal and for providing a second video signature signal and a second audio signature signal;
a signature analysis unit for receiving the first video signature signal, the first audio signature signal, the second video signature signal and the second audio signature signal and for correlating the first video signature signal with the second video signature signal to provide a video delay and for further correlating the first audio signature signal with the second audio signature signal to provide an audio delay, said signature analysis unit for further comparing said audio delay with said video delay and for providing an indication of a lip sync is said audio delay is different from said video delay,
wherein correlating the first video signature signal with the second video signature to provide a video delay comprises performing a convolution of the first video signature signal and second video signature signal to generate a first convolution signal, and determining a video matching factor inversely proportional to a minimum value of the first convolution signal divided by a sum of one of the first and second video signature signals, wherein the first video signature signal and second video signature signal are correlated if the value of the video matching factor is above a first predetermined threshold, and
wherein correlating the first audio signature signal with the second audio signature to provide an audio delay comprises performing a convolution of the first audio signature signal and second audio signature signal to generate a second convolution signal, and determining an audio matching factor inversely proportional to a minimum value of the second convolution signal divided by a size of one of the first and second audio signature signals, wherein the first audio signature signal and second audio signature signal are correlated if the value of the audio matching factor is above a second predetermined threshold;
wherein said first signature extraction unit comprises a first audio signature extraction unit for receiving said first audio signal and for providing said first audio signature signal, further wherein said first signature extraction unit comprises a first video signature extraction unit for receiving said first video signal and for providing said first video signature signal further wherein said first audio signature extraction unit comprises:
a first filtering unit for receiving the first audio signal and for providing a first filtered signal;
a second filtering unit for receiving the first audio signal and for providing a second filtered signal;
a comparator for receiving the first filtered signal and the second filtered signal and for performing a comparison of the first filtered with the second filtered signal and for providing a comparison result to thereby provide the first audio signature signal.

16. An apparatus for providing an indication of a lip sync, the apparatus comprising:
a first signature extraction unit for receiving a first audio signal and a first video signal and for providing a first video signature signal and a first audio signature signal;
a second signature extraction unit for receiving a second audio signal and a second video signal and for providing a second video signature signal and a second audio signature signal;
a signature analysis unit for receiving the first video signature signal, the first audio signature signal, the second video signature signal and the second audio signature signal and for correlating the first video signature signal with the second video signature signal to provide a video delay and for further correlating the first audio signature signal with the second audio signature signal to provide an audio delay, said signature analysis unit for further comparing said audio delay with said video delay and for providing an indication of a lip sync is said audio delay is different from said video delay,
wherein correlating the first video signature signal with the second video signature to provide a video delay comprises performing a convolution of the first video signature signal and second video signature signal to generate a first convolution signal, and determining a video matching factor inversely proportional to a minimum value of the first convolution signal divided by a sum of one of the first and second video signature signals, wherein the first video signature signal and second video signature signal are correlated if the value of the video matching factor is above a first predetermined threshold, and
wherein correlating the first audio signature signal with the second audio signature to provide an audio delay comprises performing a convolution of the first audio signature signal and second audio signature signal to generate a second convolution signal, and determining an audio matching factor inversely proportional to a minimum value of the second convolution signal divided by a size of one of the first and second audio signature signals, wherein the first audio signature signal and second audio signature signal are correlated if the value of the audio matching factor is above a second predetermined threshold;
wherein said first signature extraction unit comprises a first audio signature extraction unit for receiving said first audio signal and for providing said first audio signature signal, further wherein said first signature extraction unit comprises a first video signature extraction unit for receiving said first video signal and for providing said first video signature signal; and
wherein said first video signature extraction unit comprises:
a first image pixel data providing unit for receiving said first video signal and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image of said first video signal;
a second image pixel data providing unit for receiving said first video signal and for providing a corresponding pixel data Ck of the corresponding given pixel k in a second image of said first video signal;
a comparator for receiving the corresponding pixel data Pk and the corresponding pixel data Ck and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck to provide a result signal indicative of the comparison;
a counter for receiving and counting the result signal of each of the plurality of given pixels 1 to N and for providing a counter signal; and
a video signature providing unit for receiving the counter signal and for providing the first video signature signal.

17. An apparatus for providing an indication of a lip sync, the apparatus comprising:
a first signature extraction unit for receiving a first audio signal and a first video signal and for providing a first video signature signal and a first audio signature signal;
a second signature extraction unit for receiving a second audio signal and a second video signal and for providing a second video signature signal and a second audio signature signal;
a signature analysis unit for receiving the first video signature signal, the first audio signature signal, the second video signature signal and the second audio signature signal and for correlating the first video signature signal with the second video signature signal to provide a video delay and for further correlating the first audio signature signal with the second audio signature signal to provide an audio delay, said signature analysis unit for further comparing said audio delay with said video delay and for providing an indication of a lip sync is said audio delay is different from said video delay,
wherein correlating the first video signature signal with the second video signature to provide a video delay comprises performing a convolution of the first video signature signal and second video signature signal to generate a first convolution signal, and determining a video matching factor inversely proportional to a minimum value of the first convolution signal divided by a sum of one of the first and second video signature signals, wherein the first video signature signal and second video signature signal are correlated if the value of the video matching factor is above a first predetermined threshold, and
wherein correlating the first audio signature signal with the second audio signature to provide an audio delay comprises performing a convolution of the first audio signature signal and second audio signature signal to generate a second convolution signal, and determining an audio matching factor inversely proportional to a minimum value of the second convolution signal divided by a size of one of the first and second audio signature signals, wherein the first audio signature signal and second audio signature signal are correlated if the value of the audio matching factor is above a second predetermined threshold;
wherein said second signature extraction unit comprises a second audio signature extraction unit for receiving said second audio signal and for providing said second audio signature signal, further wherein said second signature extraction unit comprises a second video signature unit for receiving said second video signal and for providing said second video signature signal;
wherein said second audio signature extraction unit comprises:
a first filtering unit for receiving the second audio signal and for providing a first filtered signal;
a second filtering unit for receiving the second audio signal and for providing a second filtered signal;
a comparator for receiving the first filtered signal and the second filtered signal and for performing a comparison of the first filtered with the second filtered signal and for providing a comparison result to thereby provide the second audio signature signal.

18. An apparatus for providing an indication of a lip sync, the apparatus comprising:
a first signature extraction unit for receiving a first signal and first video signal and for providing a first video signature signal and a first audio signature signal;
a second signature extraction unit for receiving a second audio signal and a second video signal and for providing a second video signature signal and a second audio signature signal;
a signature analysis unit for receiving the first video signature signal, the first audio signature signal, the second video signature signal and the second audio signature signal and for correlating the first video signature signal with the second video signature signal to provide a video delay and for further correlating the first audio signature signal with the second audio signature signal to provide an audio delay, said signature analysis unit for further comparing said audio delay with said video delay and for providing an indication of a lip sync is said audio delay is different from said video delay,
wherein correlating the first video signature signal with the second video signature to provide a video delay comprises performing a convolution of the first video signature signal and second video signature signal to generate a first convolution signal, and determining a video matching factor inversely proportional to a minimum value of the first convolution signal divided by a sum of one of the first and second video signature signals, wherein the first video signature signal and second video signature signal are correlated if the value of the video matching factor is above a first predetermined threshold, and
wherein correlating the first audio signature signal with the second audio signature to provide an audio delay comprises performing a convolution of the first audio signature signal and second audio signature signal to generate a second convolution signal, and determining an audio matching factor inversely proportional to a minimum value of the second convolution signal divided by a size of one of the first and second audio signature signals, wherein the first audio signature signal and second audio signature signal are correlated if the value of the audio matching factor is above a second predetermined threshold;
wherein said second signature extraction unit comprises a second audio signature extraction unit for receiving said second audio signal and for providing said second audio signature signal, further wherein said second signature extraction unit comprises a second video signature unit for receiving said second video signal and for providing said second video signature signal;
wherein said second video signature extraction unit comprises:
a first image pixel data providing unit for receiving said second video signal and for providing a corresponding pixel data Pk of a pixel k of a plurality of given pixels 1 to N of a first image of said second video signal;
a second image pixel data providing unit for receiving said second video signal and for providing a corresponding pixel data Ck of the corresponding given pixel k in a second image of said second video signal;
a comparator for receiving the corresponding pixel data Pk and the corresponding pixel data Ck and for comparing the corresponding pixel data Pk with the corresponding pixel data Ck to provide a result signal indicative of the comparison;
a counter for receiving and counting the result signal of each of the plurality of given pixels 1 to N and for providing a counter signal; and
a video signature providing unit for receiving the counter signal and for providing the second video signature signal.