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HTML

              
                #root
              
            
!

CSS

              
                .App {
  font-family: sans-serif;
  text-align: center;
}

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  display: grid;
  place-items: center;
}
              
            
!

JS

              
                const { XState, XStateReact, React, ReactDOM } = window

const { createMachine, assign, send: sendUtil } = XState
const { useMachine } = XStateReact

function assertNonNull<PossibleNullType>(
  possibleNull: PossibleNullType,
  errorMessage: string
): asserts possibleNull is Exclude<PossibleNullType, null> {
  if (possibleNull === null) throw new Error(errorMessage);
}

const devTools = false;

// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
if (devTools && typeof window !== "undefined") {
  inspect({ iframe: false });
}

function stopMediaRecorder(mediaRecorder: MediaRecorder) {
  if (mediaRecorder.state !== "inactive") mediaRecorder.stop();

  for (const track of mediaRecorder.stream.getAudioTracks()) {
    if (track.enabled) track.stop();
  }
  mediaRecorder.ondataavailable = null;
}

interface RecorderContext {
  mediaRecorder: MediaRecorder | null;
  audioDevices: Array<MediaDeviceInfo>;
  selectedAudioDevice: MediaDeviceInfo | null;
  audioBlob: Blob | null;
}

const recorderMachine = createMachine<RecorderContext>(
  {
    id: "recorder",
    context: {
      mediaRecorder: null,
      audioDevices: [],
      selectedAudioDevice: null,
      audioBlob: null
    },
    initial: "gettingDevices",
    states: {
      gettingDevices: {
        invoke: {
          src: "getDevices",
          onDone: { target: "ready", actions: "assignAudioDevices" },
          onError: "" // TODO
        }
      },
      selecting: {
        on: {
          selection: { target: "ready", actions: "assignSelectedAudioDevice" }
        }
      },
      ready: {
        on: {
          changeDevice: "selecting",
          start: "recording"
        }
      },
      recording: {
        invoke: { src: "mediaRecorder" },
        initial: "playing",
        states: {
          playing: {
            on: {
              mediaRecorderCreated: {
                actions: ["assignMediaRecorder"]
              },
              pause: {
                target: "paused",
                actions: sendUtil("pause", { to: "mediaRecorder" })
              },
              stop: "stopping"
            }
          },
          paused: {
            on: {
              resume: {
                target: "playing",
                actions: sendUtil("resume", { to: "mediaRecorder" })
              },
              stop: "stopping"
            }
          },
          stopping: {
            entry: sendUtil("stop", { to: "mediaRecorder" }),
            on: {
              chunks: { target: "#recorder.done", actions: "assignAudioBlob" }
            }
          }
        }
      },
      done: {
        on: {
          restart: "ready"
        }
      }
    }
  },
  {
    services: {
      getDevices: async () => {
        const devices = await navigator.mediaDevices.enumerateDevices();
        return devices.filter(({ kind }) => kind === "audioinput");
      },
      mediaRecorder: (context) => (sendBack, receive) => {
        let mediaRecorder: MediaRecorder;

        async function go() {
          const chunks: Array<BlobPart> = [];
          const deviceId = context.selectedAudioDevice?.deviceId;
          const audio = deviceId ? { deviceId: { exact: deviceId } } : true;
          const mediaStream = await window.navigator.mediaDevices.getUserMedia({
            audio
          });
          mediaRecorder = new MediaRecorder(mediaStream);
          sendBack({ type: "mediaRecorderCreated", mediaRecorder });

          mediaRecorder.ondataavailable = (event) => {
            chunks.push(event.data);
            console.info('running')
            if (mediaRecorder.state === "inactive") {
              sendBack({
                type: "chunks",
                blob: new Blob(chunks, {
                  type: "audio/mp3"
                })
              });
            }
          };

          mediaRecorder.start();

          receive((event) => {
            if (event.type === "pause") {
              mediaRecorder.pause();
            } else if (event.type === "resume") {
              mediaRecorder.resume();
            } else if (event.type === "stop") {
              mediaRecorder.stop();
            }
          });
        }

        void go();

        return () => {
          stopMediaRecorder(mediaRecorder);
        };
      }
    },
    actions: {
      assignAudioDevices: assign({
        audioDevices: (context, event) => event.data
      }),
      assignSelectedAudioDevice: assign({
        selectedAudioDevice: (context, event) => event.selectedAudioDevice
      }),
      assignMediaRecorder: assign({
        mediaRecorder: (context, event) => event.mediaRecorder
      }),
      assignAudioBlob: assign({
        audioBlob: (context, event) => event.blob
      })
    }
  }
);

function CallRecorder({
  onRecordingComplete
}: {
  onRecordingComplete: (audio: Blob) => void;
}) {
  const [state, send] = useMachine(recorderMachine, { devTools });
  const { audioBlob } = state.context;

  const audioURL = React.useMemo(() => {
    if (audioBlob) {
      return window.URL.createObjectURL(audioBlob);
    } else {
      return null;
    }
  }, [audioBlob]);

  let deviceSelection = null;
  if (state.matches("gettingDevices")) {
    deviceSelection = <div>Loading devices</div>;
  }

  if (state.matches("selecting")) {
    deviceSelection = (
      <div>
        Select your device:
        <ul>
          {state.context.audioDevices.length
            ? state.context.audioDevices.map((device) => (
                <li key={device.deviceId}>
                  <button
                    onClick={() => {
                      send({
                        type: "selection",
                        selectedAudioDevice: device
                      });
                    }}
                    style={{
                      fontWeight:
                        state.context.selectedAudioDevice === device
                          ? "bold"
                          : "normal"
                    }}
                  >
                    {device.label}
                  </button>
                </li>
              ))
            : "No audio devices found"}
        </ul>
      </div>
    );
  }

  let audioPreview = null;
  if (state.matches("done")) {
    assertNonNull(
      audioURL,
      `The state machine is in "stopped" state but there's no audioURL. This should be impossible.`
    );
    assertNonNull(
      audioBlob,
      `The state machine is in "stopped" state but there's no audioBlob. This should be impossible.`
    );
    audioPreview = (
      <div>
        <audio src={audioURL} controls />
        <button onClick={() => onRecordingComplete(audioBlob)}>Accept</button>
        <button onClick={() => send({ type: "restart" })}>Re-record</button>
      </div>
    );
  }

  return (
    <div>
      {state.matches("ready") ? (
        <button onClick={() => send({ type: "changeDevice" })}>
          Change audio device from{" "}
          {state.context.selectedAudioDevice?.label ?? "default"}
        </button>
      ) : null}
      {deviceSelection}
      {state.matches("ready") ? (
        <button onClick={() => send({ type: "start" })}>Start</button>
      ) : null}
      {state.matches("recording") && state.context.mediaRecorder ? (
        <StreamVis stream={state.context.mediaRecorder.stream} />
      ) : null}
      {state.matches("recording.playing") ? (
        <>
          <button onClick={() => send({ type: "stop" })}>Stop</button>
          <button onClick={() => send({ type: "pause" })}>Pause</button>
        </>
      ) : state.matches("recording.paused") ? (
        <>
          <button onClick={() => send({ type: "stop" })}>Stop</button>
          <button onClick={() => send({ type: "resume" })}>Resume</button>
        </>
      ) : state.matches("recording.stopping") ? (
        <div>Processing...</div>
      ) : null}
      {audioPreview}
    </div>
  );
}

function visualize(canvas: HTMLCanvasElement, stream: MediaStream) {
  const audioCtx = new AudioContext();
  const canvasCtx = canvas.getContext("2d");

  const source = audioCtx.createMediaStreamSource(stream);

  const analyser = audioCtx.createAnalyser();
  analyser.fftSize = 2048;
  const bufferLength = analyser.frequencyBinCount;
  const dataArray = new Uint8Array(bufferLength);

  source.connect(analyser);

  function draw() {
    if (!canvasCtx) return;
    const WIDTH = canvas.width;
    const HEIGHT = canvas.height;

    analyser.getByteTimeDomainData(dataArray);

    canvasCtx.fillStyle = "rgb(180, 180, 180)";
    canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);

    canvasCtx.lineWidth = 2;
    canvasCtx.strokeStyle = "rgb(0, 0, 0)";

    canvasCtx.beginPath();

    const sliceWidth = (WIDTH * 1.0) / bufferLength;
    let x = 0;

    for (let i = 0; i < bufferLength; i++) {
      const v = (dataArray[i] ?? 0) / 128.0;
      const y = (v * HEIGHT) / 2;

      if (i === 0) {
        canvasCtx.moveTo(x, y);
      } else {
        canvasCtx.lineTo(x, y);
      }

      x += sliceWidth;
    }

    canvasCtx.lineTo(canvas.width, canvas.height / 2);
    canvasCtx.stroke();
  }

  return draw;
}

function StreamVis({ stream }: { stream: MediaStream }) {
  const canvasRef = React.useRef<HTMLCanvasElement | null>(null);

  React.useEffect(() => {
    if (!canvasRef.current) return () => {};
    const draw = visualize(canvasRef.current, stream);
    let lastReq: number;
    function reqDraw() {
      lastReq = requestAnimationFrame(() => {
        draw();
        reqDraw();
        // TODO: this happens too frequently...
      });
    }
    reqDraw();
    return () => {
      cancelAnimationFrame(lastReq);
    };
  }, [stream]);
  return <canvas ref={canvasRef} />;
}

ReactDOM.render(
  <CallRecorder
    onRecordingComplete={(...args) => console.log("complete", ...args)}
  />,
  document.getElementById("root")
);

              
            
!
999px

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