I have to disagree in the sense that .....

when i I last did something like this I found about 1mb was the limit .....

when was was the last time you had a significant problem uploading a 4mb photo ?

yes the browser will do it in chunks regardless of any fluctuations in available bandwidth at any given moment it all happens smoothly and 'swiftly'

i have been unable to do this on DF with web services due to the data flow NOT stopping when DF times out and have therefore had to implement 'crude' work arounds of waiting 2mins on a 4422 error, then checking did the data get there via different call, then and only then resend if it didn't make it

having your bandwidth fluctuate 500kbos to 100kbps due to traffic/shaping makes a big difference to this type of problem