1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _dv-timings: 4 5************************** 6Digital Video (DV) Timings 7************************** 8 9The video standards discussed so far have been dealing with Analog TV 10and the corresponding video timings. Today there are many more different 11hardware interfaces such as High Definition TV interfaces (HDMI), VGA, 12DVI connectors etc., that carry video signals and there is a need to 13extend the API to select the video timings for these interfaces. Since 14it is not possible to extend the :ref:`v4l2_std_id <v4l2-std-id>` 15due to the limited bits available, a new set of ioctls was added to 16set/get video timings at the input and output. 17 18These ioctls deal with the detailed digital video timings that define 19each video format. This includes parameters such as the active video 20width and height, signal polarities, frontporches, backporches, sync 21widths etc. The ``linux/v4l2-dv-timings.h`` header can be used to get 22the timings of the formats in the :ref:`cea861` and :ref:`vesadmt` 23standards. 24 25To enumerate and query the attributes of the DV timings supported by a 26device applications use the 27:ref:`VIDIOC_ENUM_DV_TIMINGS` and 28:ref:`VIDIOC_DV_TIMINGS_CAP` ioctls. To set 29DV timings for the device applications use the 30:ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl and to get 31current DV timings they use the 32:ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl. To detect 33the DV timings as seen by the video receiver applications use the 34:ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl. 35 36When the hardware detects a video source change (e.g. the video 37signal appears or disappears, or the video resolution changes), then 38it will issue a `V4L2_EVENT_SOURCE_CHANGE` event. Use the 39:ref:`ioctl VIDIOC_SUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` and the 40:ref:`VIDIOC_DQEVENT` to check if this event was reported. 41 42If the video signal changed, then the application has to stop 43streaming, free all buffers, and call the :ref:`VIDIOC_QUERY_DV_TIMINGS` 44to obtain the new video timings, and if they are valid, it can set 45those by calling the :ref:`ioctl VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>`. 46This will also update the format, so use the :ref:`ioctl VIDIOC_G_FMT <VIDIOC_G_FMT>` 47to obtain the new format. Now the application can allocate new buffers 48and start streaming again. 49 50The :ref:`VIDIOC_QUERY_DV_TIMINGS` will just report what the 51hardware detects, it will never change the configuration. If the 52currently set timings and the actually detected timings differ, then 53typically this will mean that you will not be able to capture any 54video. The correct approach is to rely on the `V4L2_EVENT_SOURCE_CHANGE` 55event so you know when something changed. 56 57Applications can make use of the :ref:`input-capabilities` and 58:ref:`output-capabilities` flags to determine whether the digital 59video ioctls can be used with the given input or output. 60