[FFmpeg-devel] PATCH grab.c, adding support for hardware based VIDIOSFPS
Mon Jun 4 19:49:21 CEST 2007
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:
> 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
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
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