Problem with using gst-launch (with avidemux and videoconvert)

[Ian Davidson]

This example is purely a test - what I really want to do is to take 
snapshots using a live camera, but on this machine I do not have a 
camera.  I think that pngenc might be useful to make my snapshots.

I ran this pipeline - but it did not work.  It seems that avidemux 
cannot link to videoconvert (see trace below).

Should I include some caps between avidemux and videoconvert?  How 
should I know what caps to choose?

Your help is appreciated.

gst-launch-1.0 --gst-debug=4,*demux*:9 filesrc 
location=~/Videos/Fri25-1323.avi ! avidemux ! videoconvert ! 
'video/x-raw,format=(string)RGB,width=640,height=480' ! pngenc 
snapshot=true ! filesink location=snap1.png

0:00:00.133311389 12835  0x8ce3c40 INFO            GST_PIPELINE 
./grammar.y:576:gst_parse_perform_link: linking avidemux0:(any) to 
videoconvert0:(any) (0/0) with caps "(NULL)"
0:00:00.133358010 12835  0x8ce3c40 INFO        GST_ELEMENT_PADS 
gstutils.c:1543:gst_element_link_pads_full: trying to link element 
avidemux0:(any) to element videoconvert0:(any)
0:00:00.133424171 12835  0x8ce3c40 INFO                GST_PADS 
gstpad.c:3583:gst_pad_peer_query:<videoconvert0:src> pad has no peer
0:00:00.133744332 12835  0x8ce3c40 INFO        GST_ELEMENT_PADS 
gstelement.c:891:gst_element_get_static_pad: no such pad 'video_%u' in 
element "avidemux0"
0:00:00.133830276 12835  0x8ce3c40 INFO        GST_ELEMENT_PADS 
gstutils.c:1123:gst_element_get_compatible_pad:<avidemux0> Could not 
find a compatible pad to link to videoconvert0:sink
0:00:00.133869855 12835  0x8ce3c40 INFO                 default 
gstutils.c:1889:gst_element_link_pads_filtered: Could not link pads: 
avidemux0:(null) - videoconvert0:(null)
-- 
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Ian Davidson