Methods and apparatus to perform audio watermarking and watermark detection and extraction
Methods and apparatus to audio watermarking and watermark detection and extracted are described herein. An example method includes receiving a media content signal, sampling the media content signal to generate samples, storing the samples in a buffer, determining a first sequence of samples in the buffer, determining a second sequence of samples in the buffer, wherein the second sequence of samples is of substantially equal length as the first sequence of samples, calculating an average of the first sequence of samples and the second sequence of samples to generate an average sequence of samples, extracting an identifier from the average sequence of samples, and storing the identifier in a tangible memory.
1. A method to extract an identifier embedded in media, the method comprising:
receiving a media signal, the media signal including at least one of an audio signal or a video signal;
determining if the media signal includes noise that exceeds a noise threshold;
in response to determining that the media signal exceeds the noise threshold, combining, by executing an instruction with at least one processor, a first sequence of samples of the media and a second sequence of samples of the media to generate an averaged sequence of samples, ones of the averaged sequence of samples having respective amplitudes based on averages of (i) amplitudes of corresponding ones of the first sequence of samples and (ii) amplitudes of corresponding ones of the second sequence of samples, the embedded identifier repeated in the media based on a repetition period, a start of the second sequence of samples and a start of the first sequence of samples separated by the repetition period; and
analyzing, by executing an instruction with the at least one processor, a frequency spectrum of the averaged sequence of samples to extract the embedded identifier from the media.
2. The method as defined in claim 1 , wherein the combining of the first sequence of samples and the second sequence of samples is performed in response to determining the embedded identifier was not extracted from a portion of the media prior to the first sequence of samples and the second sequence of samples.
3. The method as defined in claim 1 , wherein the combining of the first sequence of samples and the second sequence of samples includes summing the first sequence of samples and the second sequence of samples to generate a summed sequence of samples.
4. The method as defined in claim 3 , wherein the combining of the first sequence of samples and the second sequence of samples further includes dividing the summed sequence of samples by a number of sequences of samples used to generate the summed sequence of samples.
5. The method as defined in claim 1 , wherein the first sequence of samples and the second sequence include substantially the same number of samples.
6. The method as defined in claim 1 , wherein the analyzing includes comparing characteristics of the frequency spectrum of the averaged sequence of samples to a look-up table of characteristics.
7. The method as defined in claim 1 , further including storing the embedded identifier to meter presentation of the media.
8. The method of claim 1 , wherein the determining if the noise exceeds the noise threshold includes determining if the media signal includes significant noise that distorts the media signal.
9. An apparatus to extract an identifier embedded in media, the apparatus comprising:
at least one memory;
instructions in the apparatus; and
at least one processor to execute the instructions to at least:
determine if a media signal includes noise that exceeds a noise threshold, the media signal including at least one of an audio signal or a video signal; and
in response to a determination that the media signal includes noise that exceeds the noise threshold:
combine a first sequence of samples of the media and a second sequence of samples of the media to generate an averaged sequence of samples, ones of the averaged sequence of samples having respective amplitudes based on averages of (i) amplitudes of corresponding ones of the first sequence of samples and (ii) amplitudes of corresponding ones of the second sequence of samples, the embedded identifier repeated in the media based on a repetition period, a start of the second sequence of samples and a start of the first sequence of samples separated by the repetition period; and
analyze a frequency spectrum of the averaged sequence of samples to extract the embedded identifier from the media.
10. The apparatus as defined in claim 9 , wherein the at least one processor is to combine the first sequence of samples and the second sequence of samples in response to determining the embedded identifier was not extracted from a portion of the media prior to the first sequence of samples and the second sequence of samples.
11. The apparatus as defined in claim 9 , wherein the at least one processor is to combine the first sequence of samples and the second sequence of samples by summing the first sequence of samples and the second sequence of samples to generate a summed sequence of samples.
12. The apparatus as defined in claim 11 , wherein the at least one processor is to combine the first sequence of samples and the second sequence of samples by dividing the summed sequence of samples by a number of sequences of samples used to generate the summed sequence of samples.
13. The apparatus as defined in claim 9 , wherein the first sequence of samples and the second sequence includes substantially the same number of samples.
14. The apparatus as defined in claim 9 , wherein the at least one processor is to compare characteristics of the frequency spectrum of the averaged sequence of samples to a look-up table of characteristics.
15. The apparatus of claim 9 , wherein the embedded identifier is included in a first encoded message and a second encoded message, the embedded identifier is repeated in the media after a period of T seconds, the second sequence of samples is selected to start T seconds after a start of the first sequence of samples, and the first encoded message and the second encoded message include multiple identifiers.
16. The apparatus of claim 9 , wherein the processor is to:
compute symbol scores for respective symbols in a symbol table based on values of code frequencies in the frequency spectrum of the average sequence of samples;
select a symbol having a greatest symbol score;
determine whether the greatest symbol score satisfies a score threshold; and
store the embedded identifier if the greatest symbol score does not exceed the score threshold.
17. At least one computer readable storage disc or storage device comprising instructions that, when executed, cause at least one processor to at least:
determine if a media signal includes noise that exceeds a noise threshold, the media including at least one of an audio signal or a video signal; and
in response to determining that the media signal includes noise that exceeds the noise threshold:
combine a first sequence of samples of media and a second sequence of samples of the media to generate an averaged sequence of samples, ones of the averaged sequence of samples having respective amplitudes based on averages of (i) amplitudes of corresponding ones of the first sequence of samples and (ii) amplitudes of corresponding ones of the second sequence of samples, the media including an embedded identifier, that is repeated in the media based on a repetition period, a start of the second sequence of samples and a start of the first sequence of samples separated by the repetition period;
analyze a frequency spectrum of the averaged sequence of samples; and
extract the embedded identifier from the media.
18. The at least one computer readable storage disc or storage device as defined in claim 17 , wherein the instructions, when executed, cause the at least one processor to combine the first sequence of samples and the second sequence of samples in response to determining the embedded identifier was not extracted from a portion of the media prior to the first sequence of samples and the second sequence of samples.
19. The at least one computer readable storage disc or storage device as defined in claim 17 , wherein the instructions, when executed, cause the at least one processor to combine the first sequence of samples and the second sequence of samples by summing the first sequence of samples and the second sequence of samples to generate a summed sequence of samples.
20. The at least one computer readable storage disc or storage device as defined in claim 19 , wherein the instructions, when executed, cause the at least one processor to combine the first sequence of samples and the second sequence of samples by dividing the summed sequence of samples by a number of sequences of samples used to generate the summed sequence of samples.
21. The at least one computer readable storage disc or storage device as defined in claim 17 , wherein the first sequence of samples and the second sequence includes substantially the same number of samples.
22. The at least one computer readable storage disc or storage device as defined in claim 17 , wherein the instructions, when executed, cause the at least one processor to compare characteristics of the frequency spectrum of the averaged sequence of samples to a look-up table of characteristics.
23. The at least one computer readable storage disc or storage device as defined in claim 17 , wherein the instructions, when executed, cause the at least one processor to store the embedded identifier to meter presentation of the media.