[Libav-user] AVFilter overlay transparent image onto another transparent image

[Bryan Stewart]

ffmpeg/libav version from git-1eabd71 windows build dated: 3/25/2012

I am trying to merge two transparent images onto one another using the 
avfilter overlay:

ffmpeg -i a.png -vf movie=a.png, transpose=1 [inA]; [in] [inA] overlay [out]

a.png has alpha in the image.

When I run, the main image is always converted to yuv420p (no alpha) 
while the overlay image remains a yuva420p image.  I have tried to 
insert the format filter in front, back, etc to the source image, but 
the filter graph still inserts an extra scale filter to force the main 
image to be a yuv420p (no alpha) image.

The resulting image always has the background as my image without alpha 
and the overlay image has alpha.

Is there a way to get the main overlay image to remain an alpha image?

-- 
#-----------------------------------------------------------------#
#  Bryan C. Stewart                   Email: bstewart at ais-sim.com #
#                                     Web:   www.ais-sim.com      #
#  Advanced Interactive Systems, Inc. Phone: (831)655-0440        #
#  8 Harris Ct, Suite B5,             Fax:   (831)655-0885        #
#  Monterey, CA 93940                                             #
#-----------------------------------------------------------------#

*
*
CONFIDENTIALITY NOTICE
----------------------
This message, together with any attachments, may be legally 
privileged and is confidential information intended only for 
the use of the individual or entity to which it is addressed. 
It is exempt from disclosure under applicable law including 
court orders. If you are not the intended recipient, you are 
hereby notified that any use, dissemination, distribution or 
copy of this message, or any attachment, is strictly 
prohibited. If you have received this message in error, please 
notify the original sender and delete this message, along with
any attachments, from your computer.
In addition, Data contained in this email may be subject to the 
International Traffic in Arms Regulation (ITAR) or the Export 
Administration Regulation (EAR) of 1979. Regulated data may not 
be exported, released, or disclosed to foreign nationals inside 
or outside the United States without obtaining the prior 
written approval of Advanced Interactive Systems, Inc. and 
licenses as required by the U.S. Department of State.