Hi Folks,
I am trying to capture video from two cameras simultaneously on BB
(for stereo vision) using two USB frame grabbers. It does not work as
I would like it to be and I think the reason is USB bandwidth limit.
That is why, I thougt about converting the OTG port to host and use it
for the second frame grabber.
However, I am not sure, from electrical point of view, if the OTG port
in host mode will be using separate data transfer chanel from the main
USB hub on BB. So my question is, whether using OTG port in host mode
will help me to reach higher cummulative bandwidth?
Thank you,
Andrey.
lsusb show two different busses so i would be hopeful.
i've struggled with multiple usb cameras too. i'm tempted to
disable the check in the usb system and see how bad the result will be.
these cameras always seem to want 60% of the bandwidth so two
never work on the same bus.
it doesn't seem to be an actual bandwidth problem (as in numbers
of bits sent per unit time). it has to do with how quickly the
frame must be fetched. sounds like there is no buffering at
the camera.
i tried a more expensive usb camera (FV TouchCam N1) that supposedly
does mpeg compression. the picture is nice (720p) but the timing
constraint is the same.
network cameras would also solve the problem, for much more money.
Hi Andrew,
Thank you very much for quick response!
i've struggled with multiple usb cameras too. i'm tempted to
disable the check in the usb system and see how bad the result will be.
these cameras always seem to want 60% of the bandwidth so two
never work on the same bus.
So do you mean that cameras actually claiming more bandwidth then
required and disabling the check will let two cameras to work
together? If yes, maybe you can suggest how/where to disable this
check?
it doesn't seem to be an actual bandwidth problem (as in numbers
of bits sent per unit time). it has to do with how quickly the
frame must be fetched. sounds like there is no buffering at
the camera.
i tried a more expensive usb camera (FV TouchCam N1) that supposedly
does mpeg compression. the picture is nice (720p) but the timing
constraint is the same.
I was playing with two Logitech 9000Pro. It was slow (about 10fps),
but the bottleneck was CPU, not USB. In particular doing colorspace
conversion and using videobox elements from gstreamer to satisfy input
colorspace requirements of the DSP accelerated encoder was eating 99%
of the CPU. That is why I am currently experimenting with analog
cameras and corresponding frame grabbers which can provide exactly the
color space required by encoder.
network cameras would also solve the problem, for much more money.
Right. Also, it would not be aasy to squize everthing required (I
assume at least network hub for two cameras) into the box which is a
little bigger then BB itself 
.
Thank you very much once again!
Andrey.
> i've struggled with multiple usb cameras too. i'm tempted to
> disable the check in the usb system and see how bad the result will be.
> these cameras always seem to want 60% of the bandwidth so two
> never work on the same bus.
So do you mean that cameras actually claiming more bandwidth then
required
no probably not.
and disabling the check will let two cameras to work
together?
maybe. there might be scrambled frames. if there arent too many
then i can detect and filter them out. have to experiment.
If yes, maybe you can suggest how/where to disable this
check?
haven't done it yet. its deep kernel doodoo. unless there's a
control somewhere.