1 .. SPDX-License-Identifier: GFDL-1.1-no-invari
2
3 .. _dv-timings:
4
5 **************************
6 Digital Video (DV) Timings
7 **************************
8
9 The video standards discussed so far have been
10 and the corresponding video timings. Today the
11 hardware interfaces such as High Definition TV
12 DVI connectors etc., that carry video signals
13 extend the API to select the video timings for
14 it is not possible to extend the :ref:`v4l2_st
15 due to the limited bits available, a new set o
16 set/get video timings at the input and output.
17
18 These ioctls deal with the detailed digital vi
19 each video format. This includes parameters su
20 width and height, signal polarities, frontporc
21 widths etc. The ``linux/v4l2-dv-timings.h`` he
22 the timings of the formats in the :ref:`cea861
23 standards.
24
25 To enumerate and query the attributes of the D
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
31 current DV timings they use the
32 :ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS
33 the DV timings as seen by the video receiver a
34 :ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl.
35
36 When the hardware detects a video source chang
37 signal appears or disappears, or the video res
38 it will issue a `V4L2_EVENT_SOURCE_CHANGE` eve
39 :ref:`ioctl VIDIOC_SUBSCRIBE_EVENT <VIDIOC_SUB
40 :ref:`VIDIOC_DQEVENT` to check if this event w
41
42 If the video signal changed, then the applicat
43 streaming, free all buffers, and call the :ref
44 to obtain the new video timings, and if they a
45 those by calling the :ref:`ioctl VIDIOC_S_DV_T
46 This will also update the format, so use the :
47 to obtain the new format. Now the application
48 and start streaming again.
49
50 The :ref:`VIDIOC_QUERY_DV_TIMINGS` will just r
51 hardware detects, it will never change the con
52 currently set timings and the actually detecte
53 typically this will mean that you will not be
54 video. The correct approach is to rely on the
55 event so you know when something changed.
56
57 Applications can make use of the :ref:`input-c
58 :ref:`output-capabilities` flags to determine
59 video ioctls can be used with the given input
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