[linux-dvb] Help. VIDIOC_S_FMT

kevin liu lwtbenben at gmail.com
Fri Nov 9 04:00:17 CET 2007

Dear Markus;
    I got it. Why I have that confusion is that my usb device only
support standard NTSC(720*480), so VIDIOC_S_FMT in my driver don't
need to modify the video capture buffer.
    But I will still design the code as the usual way, maybe one day,
my hardware will support other tv norm. :-)
   You are so kind !!!
   Thank you so much.

On Nov 8, 2007 7:03 PM, Markus Rechberger <mrechberger at gmail.com> wrote:
> Hello Kevin,
> On 11/8/07, kevin liu <lwtbenben at gmail.com> wrote:
> > Dear everyone:
> >     I wonder why v4l2 driver cancel all the urbs in VIDIOC_S_FMT and
> > then reinit all the urbs to submit.
> >     VIDIOC_S_FMT only negotiate frame format with application like
> > mplayer and has nothing to do with our v4l2 driver.
> there are several ways how you can deal with that, one way would be
> that you set up the framebuffers again for a different framesize using
> While doing that setup the mode needs to be switched on the device
> depending on the device. When doing so you might bring it into an
> unstable state if you just change it while the isoc or bulk transfers
> are still running in the background.
> http://www.thedirks.org/v4l2/v4l2dev.htm
> "The size of the buffers often depends on the format of the data. For
> example, the size of capture buffers is determined by the capture
> image format set by the VIDIOC_S_FMT ioctl."
> Hope this clears up your questions, if not let me know.
> >     And in my driver I follow the way most drivers have taken, but
> > when I use usb_submit_urb() in VIDIOC_S_FMT to submit all the urbs
> > successfully reinited, my Ubuntu crashes. Caps and Scroll flash during
> > my Ubuntu crashes. I can't get any value message from my syslog.
> >
> >    Could somebody help me with this issue?
> >    Thank you in advance!
> you very likely have a bad pointer in your driver, if you can publish
> the code somewhere someone could have a look.
> regards,
> Markus

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