Me too. It keeps saying failed. I upload .mp4 files, the same that I upload to youtube. They are created with Premier Pro using the proper H.264 codec for Youtube with 1080p and 8mps bitrate. This is all standard stuff for youtube and many other platforms.
On DTube it seems to open with the upload option and starts to auto play in browser while uploading (I think that's normal) and then after a few seconds it fails and the browser tab crashes and asks to reload.

So....? anyone have an answer to this?