public boolean start(OutputStream os) {
        if (os == null) return false;
        boolean ok = true;
        closeStream = false;
        out = os;
        try {
            writeString("GIF89a"); // header
        } catch (IOException e) {
            ok = false;
        }
        return started = ok;
    }
Initiates GIF file creation on the given stream.  The stream
is not closed automatically.

@param os OutputStream on which GIF images are written.
@return false if initial write failed.
plugins/base-plugin/src/main/java/com/github/hui/quick/plugin/base/gif/GifEncoder.java