如何知道do_upload是否已经启动并完成？

I'm using CodeIgniter, and I created a form where the user can upload a video. I wanted to create a progress bar to show the user its still uploading and hides it after the upload is done. What I wanted to do is when the submit button is click it will call my loading gif and i want it to keep loading until the upload is finished. How can i detect if the upload is finish? I'm using CodeIgniter, and I created a form whe