Pixel phones have a built in background audio fingerprinting service called "Now Playing" which can operate constantly.
Shazam has an "auto shazam" feature you can enable for constant background listening, since 2016 at least!
But look into Alphonso. That's like Shazam but explicitly for covert "content recognition" listening in microphone enabled apps. And it's old.
People who say it's too expensive or impractical to do bulk listening for ad-tech just aren't paying attention.
> Pixel phones have a built in background audio fingerprinting service called "Now Playing" which can operate constantly.
That's interesting. Although can and does are very different things - appears to be a feature you turn on yourself. Upon a surface level research, I also found it to rely on an offline music fingerprint database, suggesting it doesn't retain and send off the audio it records, or metadata it extracted from them.
> Shazam has an "auto shazam" feature you can enable for constant background listening, since 2016 at least!
This is again a can vs. does difference.