Platine etape 1

app/platine-tools/sampler.ts

@@ -0,0 +1,97 @@
+class Sampler {
+  public audioContext: AudioContext = new AudioContext();
+  public gainNode: GainNode = new GainNode(this.audioContext);
+
+  public audioBuffer: AudioBuffer | null = null;
+  public audioBufferReversed: AudioBuffer | null = null;
+  public audioSource: AudioBufferSourceNode | null = null;
+
+  public duration: number = 0;
+  public isReversed: boolean = false;
+
+  constructor() {
+    this.gainNode.connect(this.audioContext.destination);
+  }
+
+  async getAudioBuffer(audioUrl: string) {
+    const response = await fetch(audioUrl);
+    const arrayBuffer = await response.arrayBuffer();
+
+    const audioBuffer = await this.audioContext.decodeAudioData(arrayBuffer);
+
+    return audioBuffer;
+  }
+
+  async loadTrack(audioUrl: string) {
+    this.audioBuffer = await this.getAudioBuffer(audioUrl);
+    this.audioBufferReversed = this.getReversedAudioBuffer(this.audioBuffer);
+
+    this.duration = this.audioBuffer.duration;
+  }
+
+  getReversedAudioBuffer(audioBuffer: AudioBuffer) {
+    const bufferArray = audioBuffer.getChannelData(0).slice().reverse();
+
+    const audioBufferReversed = this.audioContext.createBuffer(
+      1,
+      audioBuffer.length,
+      audioBuffer.sampleRate,
+    );
+
+    audioBufferReversed.getChannelData(0).set(bufferArray);
+
+    return audioBufferReversed;
+  }
+
+  changeDirection(isReversed: boolean, secondsPlayed: number) {
+    this.isReversed = isReversed;
+    this.play(secondsPlayed);
+  }
+
+  play(offset = 0) {
+    this.pause();
+
+    const buffer = this.isReversed
+      ? this.audioBufferReversed
+      : this.audioBuffer;
+
+    const cueTime = this.isReversed ? this.duration - offset : offset;
+
+    this.audioSource = this.audioContext.createBufferSource();
+    this.audioSource.buffer = buffer;
+    this.audioSource.loop = false;
+
+    this.audioSource.connect(this.gainNode);
+
+    this.audioSource.start(0, cueTime);
+  }
+
+  updateSpeed(speed: number, isReversed: boolean, secondsPlayed: number) {
+    if (!this.audioSource) {
+      return;
+    }
+
+    if (isReversed !== this.isReversed) {
+      this.changeDirection(isReversed, secondsPlayed);
+    }
+
+    const { currentTime } = this.audioContext;
+    const speedAbsolute = Math.abs(speed);
+
+    this.audioSource.playbackRate.cancelScheduledValues(currentTime);
+    this.audioSource.playbackRate.linearRampToValueAtTime(
+      Math.max(0.001, speedAbsolute),
+      currentTime,
+    );
+  }
+
+  pause() {
+    if (!this.audioSource) {
+      return;
+    }
+
+    this.audioSource.stop();
+  }
+}
+
+export default Sampler;