waveform-playlist/lib/track/loader/Loader.js

Multiple track web audio editor and player with waveform preview

import EventEmitter from "event-emitter";
export const STATE_UNINITIALIZED = 0;
export const STATE_LOADING = 1;
export const STATE_DECODING = 2;
export const STATE_FINISHED = 3;
export default class {
  constructor(src, audioContext, ee = EventEmitter()) {
    this.src = src;
    this.ac = audioContext;
    this.audioRequestState = STATE_UNINITIALIZED;
    this.ee = ee;
  }

  setStateChange(state) {
    this.audioRequestState = state;
    this.ee.emit("audiorequeststatechange", this.audioRequestState, this.src);
  }

  fileProgress(e) {
    let percentComplete = 0;

    if (this.audioRequestState === STATE_UNINITIALIZED) {
      this.setStateChange(STATE_LOADING);
    }

    if (e.lengthComputable) {
      percentComplete = e.loaded / e.total * 100;
    }

    this.ee.emit("loadprogress", percentComplete, this.src);
  }

  fileLoad(e) {
    const audioData = e.target.response || e.target.result;
    this.setStateChange(STATE_DECODING);
    return new Promise((resolve, reject) => {
      this.ac.decodeAudioData(audioData, audioBuffer => {
        this.audioBuffer = audioBuffer;
        this.setStateChange(STATE_FINISHED);
        resolve(audioBuffer);
      }, err => {
        if (err === null) {
          // Safari issues with null error
          reject(Error("MediaDecodeAudioDataUnknownContentType"));
        } else {
          reject(err);
        }
      });
    });
  }

}