[gst-devel] RFC: multi channel frame grabber card support

Farkas Levente lfarkas at bppiac.hu
Fri Apr 11 14:51:23 CEST 2008

as i wrote earlier we'd like to add support for multi channel frame 
grabber cards in gstreamer. what's the problem:
currently there are the only hardware video input supported by gstreamer 
is the v4l or v4l2 compatible video sources. there are good for common 
hardware like ip camera, tv card (with tunner) or other hardware like 
s-video input etc. but there are many kind of card which has more 
(4,8,16,24) input channel (usually analog input). there card can give 
raw or encoded video sources. but these usually has one physical devices 
ie. one /dev/videoX devices (in this case we've got n composite input). 
we'd like to build in this case n pipeline for the n input channel. one 
of the simple example IVC-100 card which has one bt878 chip and 4 
composite input and one 4 channel multiplexer.
in this case we can use v4l and choose one of the channel but we'd like 
to build 4 pipeline and set different parameters on the different 
pipeline's source properties (like frame rate, resolution etc). what's 
more we'd like to modify the source element properties during it's 
running eg. i'd like to modify the 2nd channel frame rate while wouldn't 
like to stop the other 4 pipeline!!! and it's an important feature.
what we can do?
- we can create a new source element with 4 output pads,
- or create a new source element with one output pad, but we'd like to 
create 4 such source element which can parallel use the same device's 
different input channel.
the first would be the easier, but in this case we can't modify one of 
the input channel's parameter without stop the other pipelines:-( or can 
i do it somehow? and in this case all of the pipeline has to be run in 
the same process.
in the second case we can start and stop the pipeline independently 
what's more use them in different process, but we probably have to 
create some kind of master/controller process which control the access 
of the source elements to the device.
what do you think about it?
what do you suggest about it?
what's your comments?
thanks in advance.

   Levente                               "Si vis pacem para bellum!"

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