Media identification using watermarks and signatures

An audience measurement system comprising:

• a processor and
• a memory having stored thereon machine readable instructions that, when executed by the processor, cause the audience measurement system to perform operations comprising:
• determining a media identifier characterizing a media presented by a media device, wherein the media identifier is associated with a watermark detected in the media;
• determining a first match score for a query signature and one or more first reference signatures included in a first subset of reference signatures, wherein the query signature comprises a time value within a search window determined based on a time indicated by the watermark, and wherein the first subset of reference signatures is generated from reference media associated with the media identifier;
• and
• based on determining whether the first match score satisfies a threshold, determining a second match score for the query signature and one or more second reference signatures included in a second subset of reference signatures to identify the media presented by the media device, wherein the second subset of reference signatures is different from the first subset of reference signatures.

A non-transitory machine readable storage medium comprising instructions that, when executed, cause a processor to perform operations comprising:

• determining a media identifier characterizing a media presented by a media device, wherein the media identifier is associated with a watermark detected in the media;
• determining a first match score for a query signature and one or more first reference signatures included in a first subset of reference signatures, wherein the query signature comprises a time value within a search window determined based on a time indicated by the watermark, and wherein the first subset of reference signatures is generated from reference media associated with the media identifier;
• and
• based on determining whether the first match score satisfies a threshold, determining a second match score for the query signature and one or more second reference signatures included in a second subset of reference signatures to identify the media presented by the media device, wherein the second subset of reference signatures is different from the first subset of reference signatures.