7. A method of efficiently using a battery powered device to continuously monitor an audio signal and identify audio items within the audio signal, the method including: receiving into a local cache on the battery powered device predictive audio fingerprints and corresponding audio item identifiers appropriate to a tracking mode; wherein the tracking mode includes a known or suspected alignment of at least one fingerprint extracted from the audio signal with at least one reference fingerprint, and the predictive audio fingerprints for the tracking mode are sequences of fingerprints relative to the known or suspected alignment that represent multiple candidate audio items for a single current audio item.
7. A method of efficiently using a battery powered device to continuously monitor an audio signal and identify audio items within the audio signal, the method including: receiving into a local cache on the battery powered device predictive audio fingerprints and corresponding audio item identifiers appropriate to a tracking mode; wherein the tracking mode includes a known or suspected alignment of at least one fingerprint extracted from the audio signal with at least one reference fingerprint, and the predictive audio fingerprints for the tracking mode are sequences of fingerprints relative to the known or suspected alignment that represent multiple candidate audio items for a single current audio item. 9. The method of claim 7 , further including: receiving into the local cache on the battery powered device predictive audio fingerprints and corresponding audio item identifiers appropriate to a watching mode as the device switches between the tracking and watching modes, wherein the watching mode is invoked from the tracking mode when an end of an audio item is detected or a user skips past the end of the audio item, and the predictive audio fingerprints for the watching mode are sequences of fingerprints that represent other audio items predicted as likely to follow an identified audio item; and switching between the watching mode in which a transition has occurred between the identified audio item and the single current audio item, and the tracking mode in which the multiple candidate audio items for the single current audio item have been determined, but ambiguities have not been resolved to identify the single current audio item.