code: private void decodeAudioHeader() throws IOException {
          int length = file.readInt();
          audioRate = file.readUnsignedShort();
          audioBitsPerSample = file.readUnsignedByte();
          audioChannels = file.readUnsignedByte();
  
          byte[] audioEncodingBytes = new byte[4];
          file.readFully(audioEncodingBytes);
          audioEncoding = SmjpegAudioEncoding.fromMagic(audioEncodingBytes);
  
          file.skipBytes(Math.max(0, length - 2 - 1 - 1 - 4));
      }
docs: /*Optional audio header:
  4 bytes magic - "_SND"
  Uint32 audio header length
  Uint16 audio rate
  Uint8  bits-per-sample  (8 = unsigned 8-bit audio, 16 = signed 16-bit LE audio)
  Uint8  channels         (1 = mono, 2 = stereo)
  4 bytes audio encoding  ("NONE" = none, "APCM" = ADPCM compressed)