looks like webcam lye about framerate

[John Selbie]

Webcam video capture is my business in my professional job.  I have yet 
to find a USB webcam that ships today that is not capable of 30 fps at 
640x480 resolution.  I even went to Fry's and bought some of the really 
bad $7 and and $10 webcams made by nameless Chinese companies for 
testing our product.  The pictures they produce are crappy, but they do 
indeed output 30fps!



The one surprising thing is that some UVC webcams ship with their own 
drivers that lower the frame rate for odd reasons at higher 
resolutions.  (Some of the MS Lifecams at 720p...).  But if you don't 
install the drivers that come with the cameras, then no problem (and 
it's not even an issue on Linux).



Now if you want HD and sub-HD resolutions at 30 FPS (high end MS, Logi, 
and Creative cameras), then you have pay for the high end models.  And 
most of these stream MJPG for usb bandwidth reasons.



I'll be happy to share code.



> Subject: RE: looks like webcam lye about framerate
> From: bug-track at fisher-privat.net
> To: jselbie at hotmail.com
> CC: cheese-list at gnome.org; ubuntu-qa at lists.ubuntu.com
> Date: Mon, 16 Aug 2010 07:31:41 +0200
> 
> Hi John,
> 
> thank you for your response. Yesterday late night i found that my
> worries was ...groundless.
> The output format will have written framerate in to container (ogg this
> time) but reale rate will stay same to the source. So gstreamer will not
> produce bigger file or more cpu use. Theora use dynamic frame rate and
> this is not a problem.
> 
> I will need to try your app, because even with windows by using standard
> uvc driver my cam can't produce 30 fps, only logitech driver can do it.
> 
> Regards,
> 	Alexey  
> 
> Am Sonntag, den 15.08.2010, 17:36 -0700 schrieb John Selbie:
> > 
> > Some webcams, when their aperture mode and exposure mode are set to
> > "auto", they implicitly lower their frame rate so as to allow more
> > light to be captured per frame.  I can repro this issue with both my
> > Logitech and Microsoft webcams.  On a stream configured for 30fps, the
> > frame rate can drop as low as 7fps.  As I understand it, this is "by
> > design" behavior.
> > 
> > The solution is to simply experiment with the auto-exposure switches
> > that the camera exposes through the UVC driver.  (Remember that little
> > applet I coded up and sent around - it works just great for this.
> > http://www.flickr.com/photos/selbie/4662079729/ ).  Usually by setting
> > everything to "manual".  All of these sliders and checkboxes are
> > exposed for V4L2.
> > 
> > Another workaround is to simply adjust the lighting in the room such
> > that the camera doesn't have to adjust it's virtual shutter/aperture
> > to compensate.
> > 
> > Hope this helps,
> > jrs
> > 
> > 
> > > Subject: looks like webcam lye about framerate
> > > From: bug-track at fisher-privat.net
> > > To: cheese-list at gnome.org; ubuntu-qa at lists.ubuntu.com
> > > Date: Sun, 15 Aug 2010 11:03:25 +0200
> > > 
> > > Hallo
> > > after i started to hack on performance problem by cheese i found
> > other
> > > problem with my webcams. Looks like they all lye about real frame
> > rate.
> > > You can set it to use 30 fps or 10 fps but there will be no changes
> > in
> > > image quality. The problem for cheese - with 30 fps we use more cpu
> > and
> > > make bigger files, even there is only actual 10fps stream.
> > > 
> > > Please test your cam with this command:
> > > 
> > > $(sleep 10 && killall mplayer)& mplayer -tv
> > > driver=v4l2:width=960:height=720:device=/dev/video0 tv://
> > > 
> > > change resolution according your cam. make 3 tests, first one is not
> > > always good. Find this line:
> > > v4l2: 96 frames successfully processed, 4 frames dropped.
> > > it mean i have about 10fps at resolution 960x720.
> > > 
> > > My cam should actually do 30 fps starting with resolution 640x480,
> > max
> > > what it get 10-13 fps.
> > > 
> > > Please make some test, send your feedbacks.
> > > 
> > > Regards,
> > > Alexey
> > > 
> > > _______________________________________________
> > > cheese-list mailing list
> > > cheese-list at gnome.org
> > > http://mail.gnome.org/mailman/listinfo/cheese-list
> 
> 
 		 	   		  
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