public File convert(List<File> gifs, File output) {
		String[] files = new String[gifs.size()];
		for (int i = 0; i < gifs.size(); i++) {
			File gif = gifs.get(i);
			files[i] = gif.getAbsolutePath();
		}
		String cmd = buildCommand(files, output.getAbsolutePath());
		if (runCommand(cmd))
			return output;
		else
			return null;
	}