I have brought your poster app for Mac. I would like to give you suggestion to make a better UI that is easy to understand.
It will be good if you show progress bar just below the multiple thumbnails that are generated with we drop some videos/photos on to the poster window. You can show completion status progress bar on the active upload, while for uploads that are pending, you can have a status as [Queued for upload]…
# Also please allow us to drag more videos on the same windows even if the active upload is going on.
# Also allow users to select other Queued uploads to select and delete.
If you support parallel uploads, then you can start showing the upload progress on other thumbnails.
Selecting on any thumbnail, will show the metadata on the right side. User should be able to still edit the meta data of files that have still not started to upload. Once its uploading, you can gray-out the meta data.
Your current implementation of carousel view to show upload progress is not right metaphor for uploads. It hides the upload thread. This view is good for photo viewing and not uploading.