[GEM-dev] V4L2

cyrille henry cyrille.henry at la-kitchen.fr
Tue Apr 1 22:36:43 CEST 2008


wow. 
maybe to much a hack for me.
thanks for the answer
Cyrille


Claude Heiland-Allen a écrit :
> cyrille henry wrote:
>> ok, i think i understand the problem.
>>
>>
>> i can have an image with mplayer
>> ( mplayer -tv  
>> driver=v4l2:device=/dev/video0:input=1:width=640:height=480 tv:// )
>>
>> gstreamer is also able to use this device (but only input 0, as i don't 
>> know how to change input)
>>
>> do you think there is a hack to forward this images to Gem?
> 
> This is one *really* hacky way that might work:
> 
> mkfifo stream.yuv stream.ppm
> mplayer -vo yuv4mpeg ... &
> y4mtoppm < stream.yuv > stream.ppm &
> pd -lib Gem:gridflow -open patch.pd
> 
> Gridflow can read ppm streams (which are just ppm frames concatenated 
> together.  Gridflow contains gridflow<-->pix bridge (I never got it to 
> work, though - probably I was misusing it), either that or use its 
> object to export a grid to a list.
> 
> But it might not be (probably won't be) fast enough for realtime use, I 
> only used this hack for offline transcoding from Ogg/Theora made by 
> recordmydesktop to DVD/MPEG2.
> 
> Probably not recommended,
> 
> 
> Claude
> 
>> thanks
>>
>> cyrille
>>
>> Claude Heiland-Allen a écrit :
>>> Hi,
>>>
>>> cyrille henry wrote:
>>>> i compile gem with V4L2 support, but it does not really work.
>>>> i'm really missing a (working) V4L2 support in gem. 
>>> There are so many incompatible formats (RGB, YUV, YV12, JPEG, MJPEG, 
>>> etc, ...) for V4L2, as described here:
>>>
>>> -- irc.freenode.net/#dataflow/2008-03-31 --
>>>
>>> 20:19 < wip> is gem compatible with v4l2?
>>> 20:19 < wip> cause my built-in webcam is working with 
>>> gstreamer-properties (v4l2)
>>> 20:19 < wip> but i cannot use it with gem...
>>> 20:48 < matju> wip: do you know what's the pixel format of your 
>>> camera? cause this could be the problem
>>> 20:48 < matju> wip: the V4L2 API cannot be covered by GEM, because 
>>> it's ever expanding, because Alan Cox has ruled that "format 
>>> converters" are forbidden in the Linux source code.
>>> 20:49 < matju> wip: and i mean, the V4L2 API cannot be covered by 
>>> anything at all.
>>> 20:49 < matju> wip: so you have to be lucky to have a camera that works.
>>> 20:50 < wip> matju: ic
>>> 20:50 < wip> matju: that's sad
>>> 20:51 < wip> matju: i will make some more test
>>> 20:52 < matju> wip: well, i spent just enough time on the v4l 
>>> mailing-list to understand that. after that, i didn't want to waste 
>>> time on that mailing-list. it's not for mere mortals, you know.
>>>
>>>
>>> So what is needed is a userland V4L2-support library that provides all 
>>> the format conversion stuff, as it doesn't make sense for every app to 
>>> implement them natively, but I don't know if that exists...
>>>
>>> Maybe VideoJACK would work for something like this?
>>>
>>>
>>> Claude
> 
> 
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