7.50. ioctl VIDIOC_QUERY_DV_TIMINGS¶
VIDIOC_QUERY_DV_TIMINGS - VIDIOC_SUBDEV_QUERY_DV_TIMINGS - Sense the DV preset received by the current input
ioctl(int fd, VIDIOC_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)¶
ioctl(int fd, VIDIOC_SUBDEV_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)¶
- File descriptor returned by open().
- Pointer to struct
The hardware may be able to detect the current DV timings automatically,
similar to sensing the video standard. To do so, applications call
ioctl VIDIOC_QUERY_DV_TIMINGS with a pointer to a struct
v4l2_dv_timings. Once the hardware detects
the timings, it will fill in the timings structure.
Drivers shall not switch timings automatically if new
timings are detected. Instead, drivers should send the
V4L2_EVENT_SOURCE_CHANGE event (if they support this) and expect
that userspace will take action by calling ioctl VIDIOC_QUERY_DV_TIMINGS.
The reason is that new timings usually mean different buffer sizes as
well, and you cannot change buffer sizes on the fly. In general,
applications that receive the Source Change event will have to call
ioctl VIDIOC_QUERY_DV_TIMINGS, and if the detected timings are valid they
will have to stop streaming, set the new timings, allocate new buffers
and start streaming again.
If the timings could not be detected because there was no signal, then
ENOLINK is returned. If a signal was detected, but it was unstable and
the receiver could not lock to the signal, then
ENOLCK is returned. If
the receiver could lock to the signal, but the format is unsupported
(e.g. because the pixelclock is out of range of the hardware
capabilities), then the driver fills in whatever timings it could find
ERANGE. In that case the application can call
ioctl VIDIOC_DV_TIMINGS_CAP, VIDIOC_SUBDEV_DV_TIMINGS_CAP to compare the
found timings with the hardware’s capabilities in order to give more
precise feedback to the user.
7.50.5. Return Value¶
On success 0 is returned, on error -1 and the
errno variable is set
appropriately. The generic error codes are described at the
Generic Error Codes chapter.
- Digital video timings are not supported for this input or output.
- No timings could be detected because no signal was found.
- The signal was unstable and the hardware could not lock on to it.
- Timings were found, but they are out of range of the hardware capabilities.