[GEM-dev] V4L2

Claude Heiland-Allen claudiusmaximus at goto10.org
Tue Apr 1 21:43:35 CEST 2008


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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