Gosh a weird thing has just happened. That blue bar that advances across the upload box (which indicates the progress of the upload) has suddenly shrunk back to the beginning and disappeared. Bizarre.

Edit: And now the blue bar has started again. And close to the same time, the same file had been transferring to SS via FTP and was over 20% and then dropped down to about 2%. Weird. Meanwhile the upload of that very same file at Pond 5 seems unaffected.

Update: And now Pond 5's uploader has disappeared. The website reverted back to my existing uploads with no sign of the new file that I had been uploading. I just hope Pond 5 uses FTP as well. I'm sick of these integrated website uploaders - they can't be trusted for large video files.

My gosh, it's finally worked, despite all those setbacks. It took all day but my 4k video was successfully uploaded to Videoblocks and SS. I gave up on Pond 5 for the time being. I might try P5 again tomorrow.