Choosing the tumbnail from the video also didnt work for me and had to save the thumbnail to my pc and upload it. not very convenient and confusing, but they also released there service just for a short while, i hope they fix it soon.

i uploaded my video as .mp4 and it was 33MB after uploading it again to Dtube, it took Dtube around a hour to convert/ and make it play. That hour was already a "scary" moment i can imagine the feeling a bit if you wait 23 hours and it still is not playing. :(