Transparent video rendering

How do you render an H.264 file (video) with a transparent background? I used the sequencer to put in a bunch of transparent pngs, (img sequence), and it renders with a black instead of transparent when I try to render an animation.

For a video with a transparent background you need to use a codec that actually supports transparency, most do not. If you need transparency you can use Quicktime Animation codec.

Why do you need transparency in the video. The particular purpose may be achieved by other means

Thanks! Um, I need transparency so that I can make a video overlay, and that’s sorta hard to do. Any suggestions?

I assume this is a template that will be combined over other video later? You can just render in QT Animation then (this is actually more or less what it was designed for). Or just keep it as a PNG sequence, that works too.

Or render a separate pass as alpha only, using that as a mask for the regular fill channel later. This way you can use regular codecs but you must keep both renders in sync. Also note that the compression may affect the quality of your alpha edge.

Thanks everyone!