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I tested It and When I receive it on a MediaLibrarySession.Callback
the method onAddMediaItems I find the extras of the requestedMetadata of the media empty

If I want to try something like: https://developer.android.com/guide/components/intents-common#PlaySearch

adb shell am start -n com.example.android.mediacontroller/.MediaAppControllerActivity --es com.example.android.mediacontroller.SEARCH "jazz?"  --es android.intent.extra.focus "vnd.android.cursor.item/genre" --es android.intent.extra.genre "jazz"

The rest of the extras are vanished.