1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 2
3 .. _dv-timings: 3 .. _dv-timings:
4 4
5 ************************** 5 **************************
6 Digital Video (DV) Timings 6 Digital Video (DV) Timings
7 ************************** 7 **************************
8 8
9 The video standards discussed so far have been 9 The video standards discussed so far have been dealing with Analog TV
10 and the corresponding video timings. Today the 10 and the corresponding video timings. Today there are many more different
11 hardware interfaces such as High Definition TV 11 hardware interfaces such as High Definition TV interfaces (HDMI), VGA,
12 DVI connectors etc., that carry video signals 12 DVI connectors etc., that carry video signals and there is a need to
13 extend the API to select the video timings for 13 extend the API to select the video timings for these interfaces. Since
14 it is not possible to extend the :ref:`v4l2_st 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 o 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. 16 set/get video timings at the input and output.
17 17
18 These ioctls deal with the detailed digital vi 18 These ioctls deal with the detailed digital video timings that define
19 each video format. This includes parameters su 19 each video format. This includes parameters such as the active video
20 width and height, signal polarities, frontporc 20 width and height, signal polarities, frontporches, backporches, sync
21 widths etc. The ``linux/v4l2-dv-timings.h`` he 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 22 the timings of the formats in the :ref:`cea861` and :ref:`vesadmt`
23 standards. 23 standards.
24 24
25 To enumerate and query the attributes of the D 25 To enumerate and query the attributes of the DV timings supported by a
26 device applications use the 26 device applications use the
27 :ref:`VIDIOC_ENUM_DV_TIMINGS` and 27 :ref:`VIDIOC_ENUM_DV_TIMINGS` and
28 :ref:`VIDIOC_DV_TIMINGS_CAP` ioctls. To set 28 :ref:`VIDIOC_DV_TIMINGS_CAP` ioctls. To set
29 DV timings for the device applications use the 29 DV timings for the device applications use the
30 :ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS 30 :ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl and to get
31 current DV timings they use the 31 current DV timings they use the
32 :ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS 32 :ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl. To detect
33 the DV timings as seen by the video receiver a 33 the DV timings as seen by the video receiver applications use the
34 :ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl. 34 :ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl.
35 35
36 When the hardware detects a video source chang 36 When the hardware detects a video source change (e.g. the video
37 signal appears or disappears, or the video res 37 signal appears or disappears, or the video resolution changes), then
38 it will issue a `V4L2_EVENT_SOURCE_CHANGE` eve 38 it will issue a `V4L2_EVENT_SOURCE_CHANGE` event. Use the
39 :ref:`ioctl VIDIOC_SUBSCRIBE_EVENT <VIDIOC_SUB 39 :ref:`ioctl VIDIOC_SUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` and the
40 :ref:`VIDIOC_DQEVENT` to check if this event w 40 :ref:`VIDIOC_DQEVENT` to check if this event was reported.
41 41
42 If the video signal changed, then the applicat 42 If the video signal changed, then the application has to stop
43 streaming, free all buffers, and call the :ref 43 streaming, free all buffers, and call the :ref:`VIDIOC_QUERY_DV_TIMINGS`
44 to obtain the new video timings, and if they a 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_T 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 : 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 47 to obtain the new format. Now the application can allocate new buffers
48 and start streaming again. 48 and start streaming again.
49 49
50 The :ref:`VIDIOC_QUERY_DV_TIMINGS` will just r 50 The :ref:`VIDIOC_QUERY_DV_TIMINGS` will just report what the
51 hardware detects, it will never change the con 51 hardware detects, it will never change the configuration. If the
52 currently set timings and the actually detecte 52 currently set timings and the actually detected timings differ, then
53 typically this will mean that you will not be 53 typically this will mean that you will not be able to capture any
54 video. The correct approach is to rely on the 54 video. The correct approach is to rely on the `V4L2_EVENT_SOURCE_CHANGE`
55 event so you know when something changed. 55 event so you know when something changed.
56 56
57 Applications can make use of the :ref:`input-c 57 Applications can make use of the :ref:`input-capabilities` and
58 :ref:`output-capabilities` flags to determine 58 :ref:`output-capabilities` flags to determine whether the digital
59 video ioctls can be used with the given input 59 video ioctls can be used with the given input or output.
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