7.50. ioctl VIDIOC_QUERY_DV_TIMINGS

7.50.1. Name

VIDIOC_QUERY_DV_TIMINGS - VIDIOC_SUBDEV_QUERY_DV_TIMINGS - Sense the DV preset received by the current input

7.50.2. Synopsis

int ioctl(int fd, VIDIOC_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)

int ioctl(int fd, VIDIOC_SUBDEV_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)

7.50.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to struct v4l2_dv_timings.

7.50.4. Description

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.

注釈

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 and returns 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.

ENODATA

Digital video timings are not supported for this input or output.

ENOLINK

No timings could be detected because no signal was found.

ENOLCK

The signal was unstable and the hardware could not lock on to it.

ERANGE

Timings were found, but they are out of range of the hardware capabilities.