need green screen basic interface explanation please

Hello,
I don’t need any explanation of how to color key and all that good stuff, because there are plenty of good tutorial videos on youtube which explain how to do that, some of them going into great detail and over an hour long. Unfortunately, none of them explain how to take a video which you have now made ‘transparent’ in the compositor, and slap it on top of another video, for example, if I have a talking head in one video, how do I overlay it on top of a video of cats doing cat things? If someone could point me to a tutorial of how to do this, I’d greatly appreciate it.

One thing that confuses me is that the output of the compositor does not appear in the video sequencer. Basically, I have two videos in the sequencer, and, using the sequencer, I can do an Over Drop blend of one video on top of the other video, but I just need the green screen to be transparent, and that doesn’t seem to be possible using just the sequencer. So okay that’s where the compositing mode comes in. In the compositing mode, I can easily get the green screen to be transparent, and I feed the ‘transparent’ output of my keying to the composite node. Now how do I specify that this ‘transparent’ (green removed) video should be overlayed on top of the other video in my sequencer? Do I have to add the other video into a node also? I see some tutorials that show how to overlay the green screen video onto a static image, but I want to overlay it onto a dynamic video.

Thanks for your advice on any ways to do this!

ps - I posted this and I got a success message but in fact it was a failure it did not post a new thread… will troubleshoot until successful…

okay, I see now that it flashed faster than I could read in very small typeface that the post needs approval by a moderator… Should probably fix that…

so I started to RTFM and such and that was helpful.
http://www.blender.org/manual/composite_nodes/introduction.html
I haven’t gotten all the way through the manual yet but to partly answer my original question, yes, I need to add another node, I basically need two input nodes, each of which is a movie, and both of them are fed into an alpha over node, the output of which is a green screen effect…
I will reformulate the rest of my question in a new thread to help keep things organized. Hopefully this is helpful to someone else who hasn’t read or understood the manual :slight_smile:

Make a scene for the vse, e.g… “Scene Edit Master”
Place the background clip below the clip you will want to cut out . Add the top clip (Overlay clip) above. DO NOT change it’s length yet!

Make another scene for generating key or alpha channel, e.g. “Scene Key 01” and make it the same length as the clip.
In this scene turn off the post processing option for sequencer (VSE) but turn on the compositor. Now only add your Overlay Clip as a source. Send it through a key node and set the colours you want to remove (blue or green etc.). Before sending it to the Output node make sure that you add an Alpha Convert node and set it to “Straight to Premultiplied”.

Back in the VSE scene “Scene Edit Master” you can Add the scene “Scene Key 01” and place it at exactly the same time as the source overlay clip, group these clips together so they stay locked in time when you move them (or trim them). Simply press tab to edit the group clip and turn off the original strip. Press tab to exit group clip and set its blend type to Alpha Over.

You should now have a keyed version of your source media.