[FFmpeg-devel] PATCH grab.c, adding support for hardware based VIDIOSFPS

[mmh]

Trent Piepho writes:
 > On Mon, 4 Jun 2007, Benoit Fouet wrote:
 > > mmh wrote:
 > > >  >
 > > >  > this is wrong.
 > > >  > from my videodev2.h:
 > > >  > #define VIDIOC_S_RDS            _IOWR ('V', BASE_VIDIOC_PRIVATE+11,
 > > >  > struct v4l2_radio_rds_set)
 > > >  >
 > > >  > i can (if i want) change the BASE_VIDIOC_PRIVATE+11 by
 > > >  > BASE_VIDIOC_PRIVATE+20
 > > >  > this ioctl will be defined, but will not do what you want...
 > > >  >
 > > >  > moreover, it can just return without any error, and lead you to believe
 > > >  > that framerate is accepted by the camera, even though this is not true...
 > 
 > Not exactly.  The size of the argument to the ioctl (struct
 > v4l2_radio_rds_set) is part of the ioctl number.  You could assign two
 > different ioctls to BASE_VIDIOC_PRIVATE+20 and they won't be the same if
 > the size of the arugment and the direction (R, W, WR) doesn't match.
 > 
 > > > #ifndef VIDIOSFPS
 > > > #define VIDIOSFPS		_IOW('v',BASE_VIDIOCPRIVATE+20, int)			/* Set fps */
 > > > #endif
 > > >
 > > yes, i really think this should be removed
 > > and, FWIW, syntax in v4l2 is, most of the time, as follows:
 > > VIDIOC_S_*
 > > i don't know if it's planned to add such a feature in future videodev
 > > version, though...
 > 
 > This isn't a v4l2 ioctl, but a v4l1 ioctl.  V4L2 uses the ioctl range 'V',
 > while v4l1 uses 'v'.  Notice the case difference.  Also BASE_VIDIOCPRIVATE
 > is the base for v4l1 private ioctls and BASE_VIDIOC_PRIVATE is the base for
 > v4l2.  It should still be VIDIOCSFPS to have correct v4l1 naming
 > conventions.
 > 
 > The whole ioctl name clash thing isn't solved by just removing the #define
 > from the ffmpeg code.  What happens if someone compiles on a kernel where
 > 'v',private+20 is SFPS and then runs on a kernel where it's something else?
 > 
 > This is why changing ioctls once they make it into the kernel isn't
 > allowed.

Thanks for explaining this to me.

Then can I for this device which support this particular behavior
integrate this type of functionality.  The only thing which I'm clear
on is that what I have done is not the correct thing to do... If
someone has a suggestion for this I would like to here it.

Marc