How do I convert a sequence of images into a movie that the filename does not start from 1?

I have a sequence of images to be converted into a movie. The only problem is that, I wanted to star开发者_如何学编程t converting image number 120 until 240 into a movie using ffmpeg but I don't know the command line for that. Is there any possible command line for this kind of case?

I grabbed frames using php-ffmpeg api and then converted it into move. Here is a sample code which shows how to grab frames

@$mov = new ffmpeg_movie($video_file_name);
if($mov->getFrameCount() > 1000) {
     //grab frames and make movie
}