Usage of 'format' in video/x-h264(any)

[vk_gst]

Hello,

I am trying to understand the usage of format in the caps - video/x-raw. 
I have the following pipeline : 
v4l2src -> queue -> video/x-raw -> h264parse -> avdec_h264 ->
gltransformation -> glimagesink

#root at linux-GP60-2PE:~# GST_DEBUG=3 gst-launch-1.0 -v -e v4l2src
device=/dev/video0 ! queue !
video/x-h264,width=640,height=480,framerate=30/1 ! h264parse ! avdec_h264  ! 
gltransformation ! glimagesink

However, the above fails with the following error: 

0:00:00.070642932 13328 0x558be86e3a10 ERROR           GST_PIPELINE
grammar.y:740:gst_parse_perform_link: could not link avdec_h264-0 to
gltransformation0
WARNING: erroneous pipeline: could not link avdec_h264-0 to
gltransformation0

I also tried setting the caps, after avdec_h264(not sure if it is the right
thing to do)

#root at linux-GP60-2PE:~# GST_DEBUG=3 gst-launch-1.0 -v -e v4l2src
device=/dev/video0 ! queue !
video/x-h264,width=640,height=480,framerate=30/1 ! h264parse ! avdec_h264  ! 
video/x-raw,width=640,height=480,framerate=30/1,format=RGBA !
gltransformation ! glimagesink

#0:00:00.065133323 13359 0x55b36ce37720 ERROR           GST_PIPELINE
grammar.y:726:gst_parse_perform_link: could not link avdec_h264-0 to
gltransformation0, gltransformation0 can't handle caps video/x-raw,
width=(int)640, height=(int)480, framerate=(fraction)30/1,
format=(string)RGBA
WARNING: erroneous pipeline: could not link avdec_h264-0 to
gltransformation0, gltransformation0 can't handle caps video/x-raw,
width=(int)640, height=(int)480, framerate=(fraction)30/1,
format=(string)RGBA

Now the source and sink pads for gltransformation and avdec_h264 supports
'video/x-raw, format=RGBA'. 

I am trying to understand how the 'format' affects the behaviour in the
above command. The below line works perfectly fine : 

#root at linux-GP60-2PE:~# GST_DEBUG=3 gst-launch-1.0 -v -e v4l2src
device=/dev/video0 ! queue !
video/x-h264,width=640,height=480,framerate=30/1 ! h264parse ! avdec_h264  
! glimagesink

Can anyone explain the behaviour here? 



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