Causes of pipeline non-transitivity?

[amindfv at mailbox.org]

Thank you, this both solves my immediate problem (missing `glcolorconvert`) as well as helps me find future issues (with -v I do see lines like "/GstPipeline:pipeline0/GstGLImageSinkBin:glimagesinkbin0/GstGLColorConvertElement").

Tom

On Sun, Apr 25, 2021 at 02:35:50PM +1000, Matthew Waters wrote:
> 
> 
> On 25/4/21 1:39 am, amindfv--- via gstreamer-devel wrote:
> > I frequently find myself confused and not knowing where to look when I'm able to build a pipeline from A->B, and a pipeline from B->C, but not from A->B->C.
> > 
> > For example, I can go from v4l2src->glupload:
> > 
> >      $ gst-launch-1.0 v4l2src ! glupload ! glimagesink
> > 
> > And I can go from glupload->glshader:
> > 
> >      $ gst-launch-1.0 videotestsrc ! glupload ! glshader fragment="\"`cat myshader.frag`\"" ! glimagesink
> > 
> > But when I try and combine the two, I get an error:
> > 
> >      $ gst-launch-1.0 v4l2src ! glupload ! glshader fragment="\"`cat myshader.frag`\"" ! glimagesink
> > 
> >      WARNING: erroneous pipeline: could not link gluploadelement0 to glfiltershader0
> > 
> > Where should I look when I hit issues like this? Is it always the case, for example, that A and B have negotiated a format that's incompatible with C? Or does it mean I need to provide more specific properties to A (or B, or C)? I don't see anything in gst-inspect that indicates they wouldn't all work together.
> 
> Add -v to gst-launch-1.0 to see the negotiated caps for successful cases.
> 
> In this case, you are probably missing a glcolorconvert element
> (automatically contained within glimagesink) or a videoconvert element as
> OpenGL only deals with RGBA buffers byt v4l2src likely produces some YUV
> format..
> 
> Cheers
> -Matt
> 
> > Thanks,
> > Tom
> > 
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> 
>