I have already asked on javascript/flash libraries for upload, which can make upload of larger files comfortable. However, there are limits which can disable the upload of larger files (PHP settings like upload_max_filesize, post_max_size, max_input_time etc.), which are sometimes given by your hosting provider.
Are there any libraries that can chunk (split) the file automatically before upload?
EDIT: found a note in another question: "So if you need to send truly large file I would say multiple posts with "transfer-encoding: chunked" (i.e chunked upload) is the way to go."
Not sure if this will help or not. But here is a post I wrote up about using / customizing Plupload. My example also uses the chunking feature of Plupload.
In the post is a link to my example code of it running and chunking files.
http://www.foliotek.com/devblog/plupload-custom-file-upload-ui/