1.8. Digital Video (DV) Timings¶
The video standards discussed so far have been dealing with Analog TV and the corresponding video timings. Today there are many more different hardware interfaces such as High Definition TV interfaces (HDMI), VGA, DVI connectors etc., that carry video signals and there is a need to extend the API to select the video timings for these interfaces. Since it is not possible to extend the v4l2_std_id due to the limited bits available, a new set of ioctls was added to set/get video timings at the input and output.
These ioctls deal with the detailed digital video timings that define
each video format. This includes parameters such as the active video
width and height, signal polarities, frontporches, backporches, sync
widths etc. The
linux/v4l2-dv-timings.h header can be used to get
the timings of the formats in the CEA-861-E and VESA DMT
To enumerate and query the attributes of the DV timings supported by a device applications use the ioctl VIDIOC_ENUM_DV_TIMINGS, VIDIOC_SUBDEV_ENUM_DV_TIMINGS and ioctl VIDIOC_DV_TIMINGS_CAP, VIDIOC_SUBDEV_DV_TIMINGS_CAP ioctls. To set DV timings for the device applications use the VIDIOC_S_DV_TIMINGS ioctl and to get current DV timings they use the VIDIOC_G_DV_TIMINGS ioctl. To detect the DV timings as seen by the video receiver applications use the ioctl VIDIOC_QUERY_DV_TIMINGS ioctl.
Applications can make use of the Input capabilities and Output capabilities flags to determine whether the digital video ioctls can be used with the given input or output.