Do you want to provide a patch?

(In reply to Sebastian Dröge (slomo) from comment #1)
> Do you want to provide a patch?

I've tried to make glshader support GRAY8 but I couldn't.
I hope to get get some clarification about where to start to do this.

From where do this element get the information about it's capabilities (RGBA) ?

(In reply to Hamdi Rakkez from comment #2)
> (In reply to Sebastian Dröge (slomo) from comment #1)
> From where do this element get the information about it's capabilities
> (RGBA) ?

From its parent class, GstGLFilter.

Adding GRAY8 to GstGLFilter class in GstStaticPadTemplate gst_gl_filter_sink_pad_template does not solve the problem.

Still other modifications are required.

Adding GRAY8 to GstGLFilter class in GstStaticPadTemplate gst_gl_filter_sink_pad_template does not solve the problem.

Still other modifications are required.

You have to select it somehow with a capsfilter or override the fixate_caps virtual method in your element to select GRAY8 instead of RGBA.

I have used a capsfilter to override caps like this :

gst-launch-1.0 videotestsrc ! video/x-raw,format=GRAY8,width=800,height=600 ! imagefreeze ! glupload ! capsfilter caps="video/x-raw(memory:GLMemory),format=GRAY8,width=800,height=600" ! glshader location=my_shader.frag ! glimagesink

But I have a link error :

ERROR           GST_PIPELINE grammar.y:617:gst_parse_perform_link: could not link capsfilter0 to glfiltershader0

That generally means you didn't do the modification correctly.  Does gst-inspect-1.0 glshader
show the GRAY8 caps?

Try running with GST_DEBUG=base*:7 to see what caps are being tried.

No in fact, I have done correctly the modification in GstGLFilter

So, gst-inspect-1.0 glshader gives :

...

Pad Templates:
  SRC template: 'src'
    Availability: Always
    Capabilities:
      video/x-raw(memory:GLMemory)
                 format: { RGBA, GRAY8 }
                  width: [ 1, 2147483647 ]
                 height: [ 1, 2147483647 ]
              framerate: [ 0/1, 2147483647/1 ]

  SINK template: 'sink'
    Availability: Always
    Capabilities:
      video/x-raw(memory:GLMemory)
                 format: { RGBA, GRAY8 }
                  width: [ 1, 2147483647 ]
                 height: [ 1, 2147483647 ]
              framerate: [ 0/1, 2147483647/1 ]

...

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