message: helpful message when no audio
diff: @@ -3,6 +3,6 @@ import { Offline } from "./Offline";
  export function OutputAudio(callback): Promise<void> {
  return Offline(callback, 0.1).then((buffer) => {
  - expect(buffer.isSilent()).to.equal(false);
  + expect(buffer.isSilent(), "no audio").to.equal(false);
  });
  }
  