On Thursday, December 23, 2010 10:02:33 Laurent Pinchart wrote:
> Hi Hans,
>
> On Monday 20 December 2010 14:09:40 Hans Verkuil wrote:
> > On Monday, December 20, 2010 13:48:51 Laurent Pinchart wrote:
> > >
> > > What if the application wants to change the resolution during capture ?
> > > It will have to stop capture, call REQBUFS(0), change the format,
> > > request buffers and restart capture. If filehandle ownership is dropped
> > > after REQBUFS(0) that will open the door to a race condition.
> >
> > That's why S_PRIORITY was invented.
>
> Right, I should implement that. I think the documentation isn't clear though.
> What is the background priority for exactly ?
As the documentation mentions, it can be used for background processes
monitoring
VBI (e.g. teletext) transmissions. I'm not aware of any such applications,
though.
PRIORITY_DEFAULT and PRIORITY_RECORD are the only two relevant prios in
practice.
> And the "unset" priority ?
Internal prio only. I think it's the value when no file handle is open.
> Are
> other applications allowed to change controls when an application has the
> record priority ?
No. Only read-only ioctls can be executed.
> In general I find the priority ioctls underspecified, that's why I haven't
> implemented them yet.
Use the prio support functions in v4l2-common. They are easy to use and do the
job.
Regards,
Hans
> On a side note, I've just tested the latest uvcvideo driver, and I've
> successfully captured video using a second application after calling
> REQBUFS(0) in a first application.
>
>
--
Hans Verkuil - video4linux developer - sponsored by Cisco
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