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