I just installed the FLVPlayer plugin and would like to know if it is possible to load YouTube video's in the player, kind of like when using the TextObject class.
I mean uploading a textfile with the YouTube video URL (and maybe width and height) that FLVPlayer picks up to load the video.
It seems I need to mod the plugin. Any tips for that?

The FLVplayer plugin is not supported for quite some time anymore (and is not the latest anyway). I don't remember if it even is able to play Youtube or other services' videos. Please refer to its website on how to possibly configure it:
http://www.longtailvideo.com/players/jw-flv-player/

I got it to work :-) It's fantastic!!
Much better than iFraming Youtube with TextObject. You get rid of the adds, what a nice bonus.
And I can mix with my self hosted video's. And skin the player. Gonna get a license.
I just did it with the TextObject, no need to install the flvplayer plugin although you could write one later to set the default options. iPad support and all, whoooo.

On image.php I just included the javascript file:
``

and than I made TextObjects like:
`
Loading the player ...

jwplayer("container").setup({
flashplayer: "_PATHTO/zp-extensions/zp-core/zp-extensions/flvplayer/player.swf",
file: "_YOUR_YOUTUBE_VIDEOPATH",
height: 360,
width: 640
});

`

Ok, that way will of course work.

! Just a warning..

Loading Youtube video's into JWPlayer only works with browsers with the Flash plugin enabled.
Setting the JW Embedder to HTML5 mode and YouTube's player will take over.. with adds :-(
On the iPad a black screen.
Damn, too good to be true.

Maybe it is easier to use the textobjects to use hte Youtube player directly. That does cover html5 as well (if the file format is already available in mp4 naturally which is not the case with older videos).