Power efficient detection of watermarks in media signals

1. A media device meter comprising:

a watermark detector to detect watermarks in a media signal; and

a watermark controller to:

activate the watermark detector to begin a first search interval;

place the watermark detector in a sleep mode upon expiration of the first search interval in response to no valid watermarks being detected during the first search interval; and

upon expiration of a first sleep interval after placing the watermark detector in the sleep mode, activating the watermark detector to begin a second search interval.

2. The media device meter of claim 1 , wherein the watermark controller is further to place the watermark detector in the sleep mode prior to expiration of the first search interval in response to detection of a first valid watermark during the first search interval.

3. The media device meter of claim 2 , wherein after the watermark detector is placed in the sleep mode in response to detecting the first valid watermark during the first search interval, the watermark controller is to cycle the watermark detector between subsequent sleep intervals and active intervals to detect subsequent watermarks in the media signal, the active intervals being based on expected locations of the subsequent watermarks in the media signal.

4. The media device meter of claim 3 , wherein the expected locations of the subsequent watermarks are based on a repetition rate associated with the subsequent watermarks.

5. The media device meter of claim 3 , wherein the subsequent sleep intervals have different durations than the first sleep interval.

6. The media device meter of claim 1 , wherein the watermark controller is to place the watermark detector in the sleep mode by at least one of asserting a control input, disabling power to the watermark detector or preventing a processor from invoking the watermark detector during the first sleep interval.

7. The media device meter of claim 1 , wherein the media device meter is implemented by a portable device.

8. A watermark detection method comprising:

initiating, by executing an instructions with a processor, a first search interval in which to attempt to detect watermarks in a media signal;

initiating, by executing an instruction with the processor, a sleep mode upon expiration of the first search interval in response to no valid watermarks being detected during the first search interval; and

upon expiration of a first sleep interval after initiation of the sleep mode, initiating, by executing an instruction with the processor, a second search interval.

9. The watermark detection method of claim 8 , further including initiating the sleep mode prior to expiration of the first search interval in response to detecting a first valid watermark during the first search interval.

10. The watermark detection method of claim 9 , further including, after initiation of the sleep mode in response to detecting the first valid watermark during the first search interval, cycling between subsequent sleep intervals and active intervals to detect subsequent watermarks in the media signal, the active intervals being based on expected locations of the subsequent watermarks in the media signal.

11. The watermark detection method of claim 10 , wherein the expected locations of the subsequent watermarks are based on a repetition rate associated with the subsequent watermarks.

12. The watermark detection method of claim 10 , wherein the subsequent sleep intervals have different durations than the first sleep interval.

13. The watermark detection method of claim 8 , wherein the initiating of the sleep mode includes at least one of asserting a control input to a watermark detector, disabling power to the watermark detector or preventing the processor from invoking the watermark detector during the first sleep interval.

14. The watermark detection method of claim 8 , wherein the processor is included in a portable device.

15. A tangible computer readable storage medium comprising computer readable instructions which, when executed, cause a processor to at least:

initiate a first search interval in which to attempt to detect watermarks in a media signal;

initiate a sleep mode upon expiration of the first search interval in response to no valid watermarks being detected during the first search interval; and

upon expiration of a first sleep interval after initiation of the sleep mode, initiate a second search interval.

16. The tangible computer readable storage medium of claim 15 , wherein the instructions, when executed, further cause the processor to initiate the sleep mode prior to expiration of the first search interval in response to detection of a first valid watermark during the first search interval.

17. The tangible computer readable storage medium of claim 16 , wherein after the initiation of the sleep mode in response to detection of the first valid watermark during the first search interval, the instructions, when executed, further cause the processor to cycle between subsequent sleep intervals and active intervals to detect subsequent watermarks in the media signal, the active intervals being based on expected locations of the subsequent watermarks in the media signal.

18. The tangible computer readable storage medium of claim 17 , wherein the expected locations of the subsequent watermarks are based on a repetition rate associated with the subsequent watermarks.

19. The tangible computer readable storage medium of claim 17 , wherein the subsequent sleep intervals have different durations than the first sleep interval.

20. The tangible computer readable storage medium of claim 15 , wherein the instructions, when executed, cause the processor to initiate the sleep mode by at least one of asserting a control input to a watermark detector, disabling power to the watermark detector or preventing the processor from invoking the watermark detector during the first sleep interval.