Linux: Export an animation with ALPHA background


i try to export an animation with an ‘invisible’ background, but it
seems all the image types i use (even PNG and Targa) don’t
export ALPHA, though i selected RGBA for the images.

I just compiled todays snapshot of blender.

How can i export files with ALPHA (background set to ‘invisible’)?

Best regards,

Render with Key or Premul instead of Sky (in the Display Buttons window F10).