Node compositor noob Q: how to render?

I’ve set up a noodle with an input video and output PNG sequence, but I don’t know how to make Blender actually render it. I’ve spent HOURS reading tutorials and wikis that explain what nodes do but gloss over how to actually render if you don’t have an animation.

Just clicking render animation gives me an empty render output window - I guess I need to set up something for it to work on? Setting the frame range isn’t enough…

Aha! Figured it out…
The noodle is ignored unless it leads to a composite output. The file output is presumably only if you want to output some of the intermediate stages to a parallel file?

I’ll add a note to this effect in the Blender wiki, 'cos it’s taken me hours to discover it. Ironically, it would have been far quicker to ignore the online help and go straight to the trial-and-error experimenting I ended up doing.

yes, and click do composite.