HarmonyOS 音频文件base64编解码问题

参考示例：

import { BusinessError } from '@ohos.base';
import { common } from '@kit.AbilityKit';
import { util } from '@kit.ArkTS';
import fs from '@ohos.file.fs';

@Entry
@Component struct base64video{
  private context = getContext(this) as common.UIAbilityContext
  private base: string = ''
  private base_1: string = ''

  encodeAudio() {
    try {
      this.context.resourceManager.getRawFileContent("ttt.m4a").then((value: Uint8Array) => {
        let rawFile = value;
        this.base = new util.Base64Helper().encodeToStringSync(rawFile)
      }).catch((error: BusinessError) => {
        console.error("getRawFileContent promise error is " + error);
      });
    } catch (error) {
      let code = (error as BusinessError).code;
      let message = (error as BusinessError).message;
      console.error(`promise getRawFileContent failed, error code: ${code}, message: ${message}.`);
    }
  }
  decodeAudio() {
    let pathDir = this.context.filesDir;
    let filePath = pathDir + `/test.m4a`
    let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
    let result = new util.Base64Helper().decodeSync(this.base);
    let writeLen = fs.writeSync(file.fd, result.buffer)
    fs.close(file)
  }

  async encodeAgain() {
    let pathDir = this.context.filesDir;
    let filePath = pathDir + `/test.m4a`
    let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
    let stat = fs.statSync(file.fd)
    let buf = new ArrayBuffer(stat.size)
    await fs.read(file.fd, buf)
    this.base_1 = new util.Base64Helper().encodeToStringSync(new Uint8Array(buf))
    fs.close(file)
  }

  decodeAgain() {
    let pathDir = this.context.filesDir;
    let filePath = pathDir + `/test_1.m4a`
    let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
    let result = new util.Base64Helper().decodeSync(this.base_1);
    let writeLen = fs.writeSync(file.fd, result.buffer)
    fs.close(file)
  }

  build(){
    Column(){
      Button('音频编码').onClick(()=>{ this.encodeAudio() })
      Button('音频解码并保存').onClick(()=>{ this.decodeAudio() })
      Button('重复编码').onClick(()=>{ this.encodeAgain() })
      Button('重复解码并保存').onClick(()=>{ this.decodeAgain() })
    }
  }
}