As I saw on network-traffic plupload is doing only a single multipart-form-data HTTP POST (chunking disabled). Chunking enabled would cause multiple HTTP POST which increases roundtrip overhead.

The effort for us is currently is too high to implement chunked-style just to have a better progress-bar. We not only need to glue together the chunks we also need to tunnel forward via "Transfer-Encoding: chunked" to our picture-service backend (we do a two hop to reach real pic-server: browser->app->pic-server).

Still let's see maybe in future we might implement the chunked style to offer better user-feedback.

BTW your reasons for not using chunking seem a little thin.  Your browser is making multiple "http" calls to upload a large file with or without chunking.  It is a pain to set up server side handling of chunking but once you do you will have solved your problem in all browsers.

On all tested cases I get only single UpdateProgress event, when the file is uploaded completely, which makes a progress bar jumping from 0% to 100% in one step pointless. I guess it is runtime constrained that UpdateProgress cannot be fired after certain bytes are sent (vs. runtime gets notified when HTTP call is done completely)? It would be really cool if updateEvent is fired after e.g. 50kb are sent.

I cannot use chunked mode as I have to adapt server picture-upload and anyway want to reduce HTTP calls (as far as I understood and can see in browser network panel, multiple calls are made to server backend when chunking is enabled).

Thanks!