There's a window of opportunity to delete things. If you upload a video, and nobody has voted on it, you can delete the steemit post associated with the video. It will effectively remove the video from your channel (although gone from your channel, it still exists if anyone has the link to it).. if the post is too old, you won't be able to delete it, it'll say "the comment is archived".

I'm hoping steemit adds a manual hide feature to remove old things from Dtube channels. I have a few expired vids (before I found out about pinning) and my channel is kinda cluttered with a few old videos that will never work again. If I can hide them one day, my channel will be a lot cleaner and all videos people click will work.