Chroma key webcam video with gstreamer

[Sérgio Agostinho]

Hey Mike,

To be honest I don't really know why it's not working, other than it was a
color space issue.

>From the console output you pasted I could see it was a capabilities
negotiation issue. From this point onwards it could either be a camera not
really supporting outputting h264, the linking between avdec_h264 and
alpha, or finally, between alpha and xvimagesink. Then I tested a pipeline
"equivalent" to yours which also failed. I started by replacing xvimagesink
with a fakesink and the pipeline started playing. Since alpha outputs raw
frames, the likeliest issue was with color space which you verified to be
true.

Regarding your other question I also have no clue, sorry.

Cheers

2015-05-08 15:13 GMT+02:00 Michael Ditum <mike at mikeditum.co.uk>:

> Hi Sergio,
>
> That worked great! Can you explain why I needed that? Doing a gst-inspect
> on the alpha element and the xvimagsink element, the xvimagesink component
> doesn't seem to specify any color spaces it can handle. What would I have
> needed to look at to know that I needed to add a videoconvert element
> between the alpha and xvimagesink?
>
> Also this seems to be using a lot of CPU which seems to all be down to the
> alpha element. I assume this is normal?
>
> Thanks for all your help,
>
> Mike
>
> On 6 May 2015 at 17:24, Sérgio Agostinho <sergio.r.agostinho at gmail.com>
> wrote:
>
>> Hi Mike,
>>
>> Try placing a videoconvert between the alpha and xvimagesink element.
>>
>> gst-launch-1.0 v4l2src device=/dev/video0 ! queue ! \
>>     video/x-h264,width=1920,height=1080,framerate=30/1 ! \
>>     h264parse ! avdec_h264 ! alpha method=green ! \
>>     *videoconvert* ! xvimagesink sync=false
>>
>>
>> Cheers
>>
>> 2015-05-06 15:35 GMT+02:00 Michael Ditum <mike at mikeditum.co.uk>:
>>
>>> Hi,
>>>
>>> I'm trying to put together a green screen application with my Logitech
>>> C910 WebCam on Fedora 21. I've managed to get 1080p30 h264 video from the
>>> webcam to be displayed with gstreamer using the following command:
>>>
>>> gst-launch-1.0 v4l2src device=/dev/video0 ! queue ! \
>>>     video/x-h264,width=1920,height=1080,framerate=30/1 ! \
>>>     h264parse ! avdec_h264 ! xvimagesink sync=false
>>>
>>> This is working great with nice and low latency. The next thing I want
>>> to do is Chroma Key-ing of the picture making certain colours transparent
>>> before I add an image / video behind the webcam picture. From what I've
>>> read I need to use the alpha filter to achieve this. From looking at
>>> gst-inspect I can see that it takes in video/x-raw and outputs video/x-raw.
>>> The avdec_h264 element outputs video/x-raw so it looks like I should be
>>> able to do:
>>>
>>> gst-launch-1.0 v4l2src device=/dev/video0 ! queue ! \
>>>     video/x-h264,width=1920,height=1080,framerate=30/1 ! \
>>>     h264parse ! avdec_h264 ! alpha method=green ! \
>>>     xvimagesink sync=false
>>>
>>> However whenever I run that command I get the following output:
>>>
>>> Setting pipeline to PAUSED ...
>>> Pipeline is live and does not need PREROLL ...
>>> Setting pipeline to PLAYING ...
>>> New clock: GstSystemClock
>>> Redistribute latency...
>>> ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Internal
>>> data flow error.
>>> Additional debug info:
>>> gstbasesrc.c(2933): gst_base_src_loop ():
>>> /GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
>>> streaming task paused, reason not-negotiated (-4)
>>> Execution ended after 0:00:00.437613774
>>> Setting pipeline to PAUSED ...
>>> Setting pipeline to READY ...
>>> Setting pipeline to NULL ...
>>> Freeing pipeline ...
>>>
>>> Can anyone tell me what I'm missing and why this isn't working correctly?
>>>
>>> Thanks in advance for any help,
>>>
>>> Mike
>>>
>>> _______________________________________________
>>> gstreamer-devel mailing list
>>> gstreamer-devel at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>>>
>>>
>>
>
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