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I've uploaded one video.... couldn't play it back. Tried to upload again, it's still not playing back. Not sure why.

You have to use (mp4) format or (WebM ) only. and dont close the tab you use it to upload until you play the video.

Sometime you must wait a little bit. When you use a mobile deveice it is not working.

To delete a video you have posted on Dtube, just log into you Steem account and find the post/video. From there you can delete it.