I am not 100 % sure but I do not think that Shazam is open source. At least on Wikipedia it is stated that it is developed by Apple. To be sure one has to see the license.
Only because it is free and on GitHub does not mean that it is open source software.
Thanks for asking. For anyone reading, the dev says:
"Unfortunately, the app cannot be made available via APK or on F-Droid in its current state because it’s missing the parts that make it work.
Shazam integration would require connecting to their servers and every way to do so requires payment.
Audd.io integration requires an API key that can also only be obtained by paying. They used to have a clause on their website that hinted at a free plan for projects that are open source and benefit society, but they have since removed it and haven’t returned my messages.
This is why it can’t be done at the moment. But I am on the lookout for a free song-recognition API, so if anyone has a suggestion, I’m all ears!"