Welcome to the uploadprogress extension example!
Click on the file field below or the "Browse" button to select a file, and then click the "Upload" button. For best results, select a large file — something over 10 MB. As the file uploads, you will see the progress bar fill up. You should also see a guess about the file's type. This uses the fileinfo extension to examine the bytes as they're being uploaded to guess the file type.
To learn more about what's going on in this example, read the code.