Media Session. Play & pause action handlers

index.js

// to add seek action handlers
if (/* can seek backward */) {
    window.navigator.mediasSession.setActionHandler('seekbackward', () => { /* your seek backward */ });
}
if (/* can seek forward */) {
    window.navigator.mediasSession.setActionHandler('seekforward', () => { /* your seek forward */ });
}

// to cancel seek action handlers
window.navigator.mediasSession.setActionHandler('seekbackward', null);
window.navigator.mediasSession.setActionHandler('seekforward', null);