Well, in all honesty, no matter where you post your work, you have to be your own copyright champion.  Once you put your work online, in any format, there's nothing keeping someone from either taking screenshots or downloading your video.  For example, in firefox, there are plugins you can get to download the video, in any format, currently playing in your browser. 
In the end, the choice is yours.  Do you share it and risk someone downloading it and/or sharing it against your wishes?  

Also, where you upload it has as much determination on your copyright being upheld.  YouTube is actually really good about pulling down material that it has found to be in violation, sometimes it just takes a little while if your stuff isn't as well known as, well, like a t.v. show. ;)

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Knowledge is knowing a tomato is a fruit. Wisdom is not putting it into a fruit salad.