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

[Tim-Philipp Müller]

On Mon, 2013-09-30 at 14:10 +0100, Ian Davidson wrote:

Hi Ian,

> 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.

Use camerabin from an application or script (not gst-launch), it handles
snapshotting and video recording for you.


> 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

You are missing a decoder. Avidemux only demuxes, then you have the
encoded video (unless the avi contains raw video, which is
rare/unlikely). Try replacing avidemux by decodebin.

Also add a videoscale after videoconvert and before your capsfilter.

Cheers
 -Tim

> 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)