Is there a good reason to do so?
You really can't prevent people to download your videos you
can only make it a little harder.

There is many applications, browser extensions and sites which allow people to download online videos and those are quite popular in these days.

I don't know if it protection can be done with DRM though.

To embed wmv you can use the following code (

 <!--[if IE]>
 <object id="WMP" classid="CLSID:6BF52A52-394A-11d3-B153-00C04F79FAA6" width="320" height="240">
 <param name="URL" value="http://example.com/videometafile.asx">
 </object>
<![endif]-->
<!--[if!IE]> <-->
<object id="WMP" type="video/x-ms-asf" data="http://example.com/videometafile.asx" width="320" height="240">
 <param name="src" value="http://example.com/videometafile.asx">
</object>
<!--> <![endif]--> 

Where videometafile.asx is a text file which contains

<asx version="3.0">
 <entry>
 <ref href="actual-video.wmv" />
 </entry>
</asx>

Additionally you may want to use some Eolas patch javascript do disable click to activate in IE.

You can't, there's a saying in the video forums. If it can be seen it can be copied and that includes even the "latest and greatest" protection schemes from Hollywood. The only thing you can expect to do is stop people that aren't going to take the time to investigate how to do it.

Embedding it is a start but a simple right click on the player will give you the source URL. Also be aware the file is usually downloaded to the temporary Internet files folder so a simple search through there and you get it too . Do a search for "no cache". FYI that will only work if the browser or whatever they are using respects it.

Using a flash player will stop most form viewing the source. You can also use something like mod-rewrite or a php script to generate a temporary filename that only works once, I can't give you any advice on how to do that because it's pretty much useless so I never spent the time to learn.

If you can download video, how come I cannot download some .swf files that I have found?

Well without specifics it would be hard to tell you why you can't download a swf file but it's certainly copyable savable etc. Most of the techniques used rely on the browser or lack of knowledge of the user. As an example there's a HTML code/image protector that relies on JS and a pseudo encrytption. Besides the fact it's burden for your users because they have to have JS enabled the image part can easily be overcome by using a specific application I have that will load a webpage as an image. It acts like a browser so the protection fails, the pseudo encryption relies on escaped characters and can easily be reversed.

There's also tools for viewing and saving online video, swf etc. Just like my image program they act like a browser but don't have the limitations of a browser and will instead allow you to save the file. In the end if all else fails you can always simply use a screen capture tool. You'll have some quality loss due to the conversion but it's minimal.

The only way to make it truly uncopyable is to not put it online or make it undesirable. Both of those of course aren't very good solutions.

What I would suggest is to instead place a logo on your video. At least if someone does download it and it gets distributed around you'll know it's yours plus you get some free advertising. If you want to go that route use a animated one (can't beleive I said that cause I hate them). There are tools avaialable for removing logos on video but they work best on opaque static ones. The larger, more animated and more obtrusive they are the harder they are to remove, only trouble with that is your users may find them less than desirable.

This is all very interesting, however it does not seem like the basic user could easily download a video if there is no save as link to the video. I have seen a lot of embedded videos that if you right mouse click on them it only brings up a menu for for example MS Media Player, but there is no way to download or save the video that way.

Ok, so, the tell me, how about youtube videos? Can anyone download them? Because all of those if you right mouse click also cannot save or download them.

Yes you are correct the average user may not be able to download them but they only have to do a quick search to find the tools to do so. Firefox has extensions for doing this and there are even webpages that will give the direct link to the file. It's just a matter of how determined they are to get the video.

Youtube uses a flash player, as I mentioned above it hides the source well but it's not fool proof.