src/remux/aac-helper.ts

/**
 *  AAC helper
 */

class AAC {
  static getSilentFrame(
    codec?: string,
    channelCount?: number
  ): Uint8Array | undefined {
    switch (codec) {
      case 'mp4a.40.2':
        if (channelCount === 1) {
          return new Uint8Array([0x00, 0xc8, 0x00, 0x80, 0x23, 0x80]);
        } else if (channelCount === 2) {
          return new Uint8Array([
            0x21, 0x00, 0x49, 0x90, 0x02, 0x19, 0x00, 0x23, 0x80,
          ]);
        } else if (channelCount === 3) {
          return new Uint8Array([
            0x00, 0xc8, 0x00, 0x80, 0x20, 0x84, 0x01, 0x26, 0x40, 0x08, 0x64,
            0x00, 0x8e,
          ]);
        } else if (channelCount === 4) {
          return new Uint8Array([
            0x00, 0xc8, 0x00, 0x80, 0x20, 0x84, 0x01, 0x26, 0x40, 0x08, 0x64,
            0x00, 0x80, 0x2c, 0x80, 0x08, 0x02, 0x38,
          ]);
        } else if (channelCount === 5) {
          return new Uint8Array([
            0x00, 0xc8, 0x00, 0x80, 0x20, 0x84, 0x01, 0x26, 0x40, 0x08, 0x64,
            0x00, 0x82, 0x30, 0x04, 0x99, 0x00, 0x21, 0x90, 0x02, 0x38,
          ]);
        } else if (channelCount === 6) {
          return new Uint8Array([
            0x00, 0xc8, 0x00, 0x80, 0x20, 0x84, 0x01, 0x26, 0x40, 0x08, 0x64,
            0x00, 0x82, 0x30, 0x04, 0x99, 0x00, 0x21, 0x90, 0x02, 0x00, 0xb2,
            0x00, 0x20, 0x08, 0xe0,
          ]);
        }

        break;
      // handle HE-AAC below (mp4a.40.5 / mp4a.40.29)
      default:
        if (channelCount === 1) {
          // ffmpeg -y -f lavfi -i "aevalsrc=0:d=0.05" -c:a libfdk_aac -profile:a aac_he -b:a 4k output.aac && hexdump -v -e '16/1 "0x%x," "\n"' -v output.aac
          return new Uint8Array([
            0x1, 0x40, 0x22, 0x80, 0xa3, 0x4e, 0xe6, 0x80, 0xba, 0x8, 0x0, 0x0,
            0x0, 0x1c, 0x6, 0xf1, 0xc1, 0xa, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5e,
          ]);
        } else if (channelCount === 2) {
          // ffmpeg -y -f lavfi -i "aevalsrc=0|0:d=0.05" -c:a libfdk_aac -profile:a aac_he_v2 -b:a 4k output.aac && hexdump -v -e '16/1 "0x%x," "\n"' -v output.aac
          return new Uint8Array([
            0x1, 0x40, 0x22, 0x80, 0xa3, 0x5e, 0xe6, 0x80, 0xba, 0x8, 0x0, 0x0,
            0x0, 0x0, 0x95, 0x0, 0x6, 0xf1, 0xa1, 0xa, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5e,
          ]);
        } else if (channelCount === 3) {
          // ffmpeg -y -f lavfi -i "aevalsrc=0|0|0:d=0.05" -c:a libfdk_aac -profile:a aac_he_v2 -b:a 4k output.aac && hexdump -v -e '16/1 "0x%x," "\n"' -v output.aac
          return new Uint8Array([
            0x1, 0x40, 0x22, 0x80, 0xa3, 0x5e, 0xe6, 0x80, 0xba, 0x8, 0x0, 0x0,
            0x0, 0x0, 0x95, 0x0, 0x6, 0xf1, 0xa1, 0xa, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a, 0x5a,
            0x5a, 0x5e,
          ]);
        }
        break;
    }
    return undefined;
  }
}

export default AAC;