Missing decoder plugin

[Orko]

Hello,

i try to use an ip camera as a webcam for my raspberry pi. there for
installed v4l2loopback and tried 
to stream the rtsp stream to /dev/video0  with the command 

gst-launch-1.0 rtspsrc location=rtsp://192.168.87.43/ ! decodebin ! v4l2sink
device=/dev/video0

But i get the following error:

Setting pipeline to PAUSED ...
libv4l2: error getting pixformat: Invalid argument
Pipeline is live and does not need PREROLL ...
Progress: (open) Opening Stream
Progress: (connect) Connecting to rtsp://192.168.87.43/
Progress: (open) Retrieving server options
Progress: (open) Retrieving media info
Progress: (request) SETUP stream 0
Progress: (open) Opened Stream
Setting pipeline to PLAYING ...
New clock: GstSystemClock
Progress: (request) Sending PLAY request
Progress: (request) Sending PLAY request
Progress: (request) Sent PLAY request
Missing element: H.264 (Main Profile) decoder
ERROR: from element /GstPipeline:pipeline0/GstDecodeBin:decodebin0: Your
GStreamer installation is missing a plug-in.
Additional debug info:
gstdecodebin2.c(4592): gst_decode_bin_expose ():
/GstPipeline:pipeline0/GstDecodeBin:decodebin0:
no suitable plugins found:
Missing decoder: H.264 (Main Profile) (video/x-h264,
stream-format=(string)avc, alignment=(string)au,
codec_data=(buffer)014d001fffe10013474d001f99a014016e8400000fa00000fa021001000448ee3c80,
level=(string)3.1, profile=(string)main)

Execution ended after 0:00:02.303332973
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
Freeing pipeline ...

I'm not sure if the problem is really the missing plugin or this "libv4l2:
error getting pixformat: Invalid argument" .
The rtsp stream is working with vlc the codec is mpeg4 avc. 
If i output to a fakesink i get the same decoding error but i have no clue
on how to fix that.
Maybe you guys have an idea of what i'm missing. 
Anyway thank you in advance.





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