Audio latency is, essentially, the time it takes for audio data to move from your projector to your Bluetooth speaker. Wired connection produces an imperceptible amount of lag—about 5-10ms worth. Within this 5-10ms window, your device processes digital audio data, converts said data to an audio signal, and streams the signal through your speak...
Please see: How to manage locally stored files on the projector
Please see: How to connect your mobile device with the projector via Bluetooth
Please see: How to Cast and Mirror your Mobile Device to the Projector