One of the great features of DEVOS is that each user "owns" their content and can control how it is used by others.
For example, you might post a video that you want to put in one of your channels but not allow others to add your video to their channels. Or maybe you post a video and you do want others to be able to add it to their channels.
To control this, you use the "Sharable" setting found under Media -> Settings on the administration page for the profile you wish to use.
You can have a profile with sharing turned on, and another profile with the sharing turned off for example. When you post or edit you video, simply select the Media Setting profile you wish.
But what happens if you put a video that is not shared to a channel you do not own?
Think about it: you have told the system NOT to share your video. So if someone with add/delete privilege tries to use your non-shared video, the system does exactly what you told it to do and it will not display the video in someone else's channel. If your video is shared, then it will display. This is why you have multiple media settings, so you can control the behavior.
Many people just use the default media setting where sharing is disabled. The good news is that you can easily change this by simply editing your default media setting to enable sharing, and all videos that use this media setting will instantly change to the new values (you don't need to go 1 by 1 to each video). Of course, you could also make a new media setting (call it "Shared" or similar), and use this media setting for the target videos.