Luma -> Alpha with v1.18

[amindfv at mailbox.org]

On Thu, Jan 06, 2022 at 01:47:17PM +0530, Nirbheek Chauhan wrote:
> On Thu, Jan 6, 2022 at 5:00 AM amindfv--- via gstreamer-devel
> <gstreamer-devel at lists.freedesktop.org> wrote:
> >
> > I'm looking for a way to use the luma plane of one video as the alpha plane of another.
> >
> > It appears the "alphacombine" element (https://gstreamer.freedesktop.org/documentation/codecalpha/alphacombine.html?gi-language=c) can do this, but it's too new even for the unstable release of GStreamer, and for a variety of reasons I'm stuck on the latest stable (1.18).
> >
> > What I'm trying to do is also possible in ffmpeg with "extractplanes=y" + "alphamerge".
> >
> > I'd welcome any way to do this, no matter how much of a hack. Big pipeline? Fine. Somehow using GPU/shaders? No prob.
> 
> You can copy the plugin's source code into your project, and then either:
> 
> 1. Build it as a dynamic plugin and set GST_PLUGIN_PATH to it, or
> 2. Link to it statically and register it manually with gst_element_register()
> 
> This is probably the easiest thing you can do. You can keep syncing
> the plugin sources with upstream till you can move to 1.20
> 

Thank you. I'm going down this path but having difficulty finding the correct way to build it.

I've made some progress with lines like the below, but I'm more or less taking shots in the dark:

    libtool --mode=link gcc `pkg-config --cflags --libs gstreamer-1.0 gobject-2.0 glib-2.0` -o gstalphacombine.o gstalphacombine.c

Am I headed in the right direction?

Thanks,
Tom