[gst-devel] Rendering mjpeg streaming video in the defined alpha channel of a jpeg

[Andres Gonzalez]

  On 26/08/10 18:58, thelenko wrote:
> What I want to do is render a crosshair image on top of a mjpeg video feed
> from a camera.  Since I am very new to gstreamer I proceeded to do this in
> baby steps, but run into issues with my mjpeg video stream.  I am going to
> outline my steps below so you can see what I tried, what worked, and where I
> got stuck:

Hi,
I am not a GStreamer expert, but recently I have been working with 
videomixer and had similar problems. That "Task paused, reason 
not-negotiated (-4)" happened a lot. It looks to me like in one of the 
branches of your pipeline (that which gnomevfssrc0 belongs to) there is 
no way to get all the elements working together, because for each thing 
the upstream elements can produce, the downstream elements can't manage 
it (don't take this too seriously, I'm just writing what I think...).
So in a few words, I think there is some element missing, possibly a 
videoscale element in some point between videomixer and gnomevfssrc0, or 
maybe between videomixer and multifilesrc. Maybe then you will also want 
to specify the capabilities (image size, for example).

Surely the big guys can correct me if I'm wrong :-)

Good luck,
Andrés




> Sorry, it is a bit of a long read.  You can probably skip to the last
> command if you desire.  Thanks in advance for your time and help :)
>
> I am able to get the video feed to properly display using the following
> command:
>
> gst-launch gnomevfssrc
> location=http://ccd1611-403/axis-cgi/mjpg/video.cgi?resolution=1280x1024 !
> decodebin ! ffmpegcolorspace ! xvimagesink
>
> I am able to display the image as a video using the following command:
>
> gst-launch multifilesrc location="crosshair.jpg"
> caps="image/jpeg,framerate=1/1" ! decodebin ! xvimagesink
>
> Taking a look at the official documents I found an example for displaying a
> video within a defined alpha channel.  The following example displays a snow
> test video in the green channel of a pattern test image:
>
> gst-launch videotestsrc pattern=smpte75 ! alpha method=green ! videomixer
> name=mix ! ffmpegcolorspace ! xvimagesink videotestsrc pattern=snow ! mix.
>
> I was able to transplant my image into the example like so:
>
> gst-launch multifilesrc location="crosshair.jpg"
> caps="image/jpeg,framerate=1/1" ! decodebin ! ffmpegcolorspace ! alphacolor
> ! alpha method=green ! queue ! videomixer name=mixer ! ffmpegcolorspace !
> xvimagesink videotestsrc pattern=snow ! mixer.
>
> I now had my cross-hair appearing on top of the snow test video.  I next
> tried to switch the snow test video with my video feed:
>
> gst-launch multifilesrc location="crosshair2.jpg"
> caps="image/jpeg,framerate=1/1" ! decodebin ! ffmpegcolorspace ! alphacolor
> ! alpha method=green ! queue ! videomixer name=mixer ! ffmpegcolorspace !
> autovideosink gnomevfssrc
> location=http://ccd1611-403/axis-cgi/mjpg/video.cgi ! decodebin !
> ffmpegcolorspace ! queue ! mixer.
>
> When I run this I get the following error:
>
> ERROR: from element /GstPipeline:pipeline0/GstGnomeVFSSrc:gnomevfssrc0:
> Internal data flow error.
> Additional debug info:
> gstbasesrc.c(2507): gst_base_src_loop ():
> /GstPipeline:pipeline0/GstGnomeVFSSrc:gnomevfssrc0:
> streaming task paused, reason not-negotiated (-4)
> ERROR: pipeline doesn't want to preroll.
>
> I assume there is something about the format of my video that it is not
> liking, but I am not sure how to remedy it.
>
> Any suggestions would be appreciated.. Thank you for your time and help :)