public void decode() throws IOException {
    if (mDecoded) {
      throw new IllegalStateException("decode called multiple times");
    }
    mDecoded = true;
    readGifInfo();
  }
@param is InputStream to decode
@param os OutputStream to write fixed version of gif, if needed. (optional)
animated-gif-lite/src/main/java/com/facebook/animated/giflite/decoder/GifMetadataDecoder.java