i want to use one rendered sequence as an alpha channel for another rendered sequence
(and then do a simple “alpha over” of the result onto my background sequence…)
this is all easy using compositing nodes,but is there a way using just the sequence editor?
so far it seems I have to combine them in the compositor…
I want to use the sequencer because of its super quick playback and am hoping for fast tweaking…
hmm, pluggin? But not sure for 2.5
Haven’t found one so far… I’m not using 2.5 for production yet…
There is a make matte pluggin but I’m not sure how to use a 3rd track as a matte key for fill and background.
That seems to allow extracting the alpha channel, not replacing it… Maybe I should download it anyway and give it a shot…
there is a plugin that convert a bw image to alpha. http://wiki.blender.org/index.php/Doc:Manual/Sequencer/Effects/Plugins and then as i say there multiply as your mix mode
I coded a layer plugin a long time ago ( just before nodes were added to blender ) that did a gimp like layer effect to strips…
If you attach all 3 strips (rendered, background, & mask render) it will do what you want in one step.
http://sites.google.com/site/papsplugins/layer.8.c
http://sites.google.com/site/papsplugins/layer.8.so (32bit linux)
Papasmurf, I couldn’t get that to work…
paprmh,that sounds ideal!
How do I compile a sequencer plugin? (I’m on linux 64bit…)
EDIT… FOund out how!
THANKYOU! this is excellent! Have you ever thought about submitting this to the plugin page?
You’re welcome, glad it’s useful for you 
No, I wouldn’t submit this to the repository because it is(/was) just a WIP that contains some sloppy & experimental code and possibly some bugs ( no crashers though- I think). I quit working on it when nodes pretty much killed off any interest in seq plugins - although I still like to use it due to the limitations of the strip blend modes.
Besides, the repository has not been properly updated for a long time… most of them are not float aware (just add a scene strip to a plugin or hit the float button in the filter tab of a strip attached to almost any plugin and blender will crash) and some are buggy.
However, if you use plugins alot, you might be interested to know that I did update a bunch of the repository plugins last spring
BTW: The info button can be useful when setting up but it can also slow the plugin down quite a bit due to the print outs to the console so turn it off when you actually process the strips.
+1 for seq pluggins! It’s the only place I can get interlace love for image processing at the moment. thanks for the effort paprmh. I think with the extra effort devoted to the sequencer via Durian, these sorts of additions will be very usefull.