Methods and apparatus to perform symbol-based watermark detection
An example symbol-based watermark detection method disclosed herein includes, in response to a comparison of a first count of occurrences of a first potential symbol value corresponding to a first symbol within a watermark and a second count of occurrences of a second potential symbol value corresponding to the first symbol, (i) determining a first accumulated signal to noise ratio value corresponding to the occurrences of the first potential symbol value, (ii) determining a second accumulated signal to noise ratio value corresponding to the occurrences of the second potential symbol value, and (iii) selecting one of the first or the second potential symbol value having a greatest accumulated signal to noise ratio value as a likely symbol value for the first symbol. The example method also includes concatenating the likely symbol value with other likely symbol values corresponding to other symbols of the watermark to detect the watermark.
1. An apparatus to perform symbol-based watermark detection, the apparatus comprising:
a symbol buffer analyzer to:
determine a first count of occurrences of a first potential symbol value within a history of potential symbol values corresponding to a first symbol within a watermark;
determine a second count of occurrences of a second potential symbol value within the history of potential symbol values corresponding to the first symbol within the watermark;
in response to a comparison of the first count of occurrences and the second count of occurrences:
determine a first accumulated signal to noise ratio value corresponding to the occurrences of the first potential symbol value;
determine a second accumulated signal to noise ratio value corresponding to the occurrences of the second potential symbol value; and
select one of the first potential symbol value or the second potential symbol value having a greatest accumulated signal to noise ratio value as a likely symbol value for the first symbol; and
a watermark constructor to concatenate the likely symbol value with other likely symbol values corresponding to other symbols of the watermark to detect the watermark.
2. The apparatus of claim 1 , further including a symbol buffer to store the history of the potential symbol values corresponding to the first symbol.
3. The apparatus of claim 2 , wherein the symbol buffer is further to store signal to noise ratio values corresponding to each of the potential symbol values.
4. The apparatus of claim 2 , wherein the symbol buffer is to store six values in each history of symbols values corresponding to each symbol of the watermark.
5. The apparatus of claim 1 , wherein the symbol buffer analyzer is further to:
determine that at least one of the first count of occurrences or the second count of occurrences exceeds an occurrence threshold;
in response to a determination that the at least one of the first count of occurrences or the second count of occurrences does not meet the occurrence threshold:
determine whether a pattern is identifiable in the history of potential symbol values; and
select one of the history of potential symbol values as the most likely symbol value when the pattern is identifiable.
6. The apparatus of claim 5 , wherein the pattern is an incrementing value corresponding to incrementing timestamps within data conveyed by the watermark.
7. The apparatus of claim 5 , wherein the symbol buffer analyzer is further to select one of the history of potential symbol values having a most recently identified symbol value that matches the pattern.
8. The apparatus of claim 1 , wherein the symbol buffer analyzer is further to determine whether the first accumulated signal to noise ratio value is greater than the second accumulated signal to noise ratio value by at least a threshold amount, and the symbol buffer analyzer is to select the first potential symbol value in response to the determination that the first accumulated signal to noise ratio value is greater than the second accumulated signal to noise ratio value by at least the threshold amount.
9. A symbol-based watermark detection method comprising:
determining, by executing an instruction with a processor of an audience measurement device, a first count of occurrences of a first potential symbol value within a history of potential symbol values corresponding to a first symbol within a watermark;
determining, by executing an instruction with the processor, a second count of occurrences of a second potential symbol value within the history of potential symbol values corresponding to the first symbol within the watermark;
in response to a comparison of the first count of occurrences and the second count of occurrences, perform first operations including:
determining, by executing an instruction with the processor, a first accumulated signal to noise ratio value corresponding to the occurrences of the first potential symbol value;
determining, by executing an instruction with the processor, a second accumulated signal to noise ratio value corresponding to the occurrences of the second potential symbol value; and
selecting, by executing an instruction with the processor, one of the first potential symbol value or the second potential symbol value having a greatest accumulated signal to noise ratio value as a likely symbol value for the first symbol; and
concatenating the likely symbol value with other likely symbol values corresponding to other symbols of the watermark to detect the watermark.
10. The method of claim 9 , further including populating a symbol buffer with the history of potential symbol values corresponding to the first symbol.
11. The method of claim 10 , further including populating signal to noise ratio values corresponding to each of the potential symbol values in the symbol buffer.
12. The method of claim 10 , further including storing six historic values of each symbol of the watermark in the symbol buffer.
13. The method of claim 9 , wherein the first operations are performed in response to the determining that (i) the first count of occurrences equals the second count of occurrences, (ii) the first count of occurrences satisfies an occurrence threshold, and (iii) the second count of occurrences satisfies the occurrence threshold, and further including:
in response to determining that at least one of the first count of occurrences or the second count of occurrences does not satisfy the occurrence threshold:
determining whether a pattern is identifiable in the history of potential symbol values corresponding to the first symbol; and
selecting one of the history of potential symbol values as the likely symbol value when the pattern is identifiable.
14. The method of claim 13 , wherein the pattern is an incrementing value corresponding to incrementing timestamps within data conveyed by the watermark.
15. The method of claim 13 , wherein the selected one of the history of potential symbol values is a most recently identified symbol value that matches the pattern.
16. The method of claim 9 , further including determining whether the first accumulated signal to noise ratio value is greater than the second accumulated signal to noise ratio value by at least a threshold amount, and the first potential symbol value is selected in response to a determination that the first accumulated signal to noise ratio value is greater than the second accumulated signal to noise ratio value by at least the threshold amount.
17. A non-transitory computer readable medium comprising instructions which, when executed, cause a machine to at least:
determine a first count of occurrences of a first potential symbol value within a history of potential symbol values corresponding to a first symbol within a watermark;
determine a second count of occurrences of a second potential symbol value within the history of potential symbol values corresponding to the first symbol within the watermark;
in response to a comparison of the first count of occurrences and the second count of occurrences:
determine a first accumulated signal to noise ratio value corresponding to occurrences of the first potential symbol value;
determine a second accumulated signal to noise ratio value corresponding to occurrences of the second potential symbol value; and
select one of the first potential symbol value or the second potential symbol value having a greatest accumulated signal to noise ratio value as a likely symbol value; and
concatenate the likely symbol value with other likely symbol values corresponding to other symbols of the watermark to detect the watermark.
18. The non-transitory computer readable medium of claim 17 , wherein the instructions, when executed, further cause the machine to populate a symbol buffer with the history of potential symbol values corresponding to the first symbol.
19. The non-transitory computer readable medium of claim 18 , wherein the instructions, when executed, further cause the machine to populate the symbol buffer with signal to noise ratio values corresponding to each of the potential symbol values.
20. The non-transitory computer readable medium of claim 18 , wherein the symbol buffer is to store six values of history of each symbol of the watermark.
21. The non-transitory computer readable medium of claim 17 , wherein the instructions, when executed, further cause the machine to, in response to a determination that (i) the first count of occurrences equals the second count of occurrences, (ii) the first count of occurrences satisfies an occurrence threshold, and (iii) the second count of occurrences satisfies the occurrences threshold:
determine whether a pattern can is identifiable in the history of potential symbol values corresponding to the first symbol; and
select one of the history of potential symbol values as the most likely symbol value when the pattern is identifiable.
22. The non-transitory computer readable medium of claim 21 , wherein the pattern is an incrementing value corresponding to incrementing timestamps within data conveyed by the watermark.
23. The non-transitory computer readable medium of claim 21 , wherein the selected one of the history of potential symbol values is a most recently identified symbol value that matches the pattern.
24. The non-transitory computer readable medium of claim 17 , wherein the instructions, when executed, further cause the machine to:
determine that the first accumulated signal to noise ratio value is greater than the second accumulated signal to noise ratio value by at least a threshold amount; and
select the first potential symbol in response to the determination that the first accumulated signal to noise ratio value is greater than the second accumulated signal to noise ratio value by at least the threshold amount.