I spent the last few weeks editing sound for my new video series. Meanwhile, to my great joy 
1. Remember to add a file extension to the name of your video.
Some programs add the file extension automatically, so you may not have to, but Final Cut (version 6.0.1) doesn't do that, so you have to type it manually. If you exported your file already, just rename it and add .mov or whatever you exported it as. Many programs are unable to identify your file unless the extension is specified. Dtube is one of them, at least for the moment.
My second attempt, once I added the file extension, was only half successful. The video uploaded but it has no sound. This was very disappointing since I had put a lot of work into it. I suspected it must have something to do with sound format.
The default sound format was set to Integer. I decided to change it and see if dtube will accept something else. Here is how to do it.
2. Change sound format of your video.
Go to File, choose Export and then choose using Quicktime Conversion. The following window pops up:
Press Options... to get to Settings:
In this window you can see the sound format is set to Integer. Click on Settings... button under Sound. Now you can select a different option from the Format menu.
In this window, the default is Linear PCM, which I changed to AAC. Linear PCM (Pulse-code modulation) is a format used in standard Audio CD's where the data is not compressed. AAC (Advanced Audio Coding) is a coding standard for lossy digital audio compression. It achieves better sound quality than MP3 at the same bit rate and it is used in MPEG-2 and MPEG-4 files. One might ask why not export the file as MPEG-4 in the first place. I tried but dtube doesn't support it at the moment.
Final Cut should remember this option, so you will not have to change the setting again. If I try exporting again, the format now says AAC.
You can press ok and save your file. Once it has finished exporting, you can upload it to dtube and share it with the world!