Documentation/media/uapi/v4l/vidioc-querystd.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_QUERYSTD:
   4
   5 *********************
   6 ioctl VIDIOC_QUERYSTD
   7 *********************
   8
   9 Name
  10 ====
  11
  12 VIDIOC_QUERYSTD - Sense the video standard received by the current input
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. cpp:function:: int ioctl( int fd, int request, v4l2_std_id *argp )
  19
  20
  21 Arguments
  22 =========
  23
  24 ``fd``
  25     File descriptor returned by :ref:`open() <func-open>`.
  26
  27 ``request``
  28     VIDIOC_QUERYSTD
  29
  30 ``argp``
  31
  32
  33 Description
  34 ===========
  35
  36 The hardware may be able to detect the current video standard
  37 automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a
  38 pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
  39 stores here a set of candidates, this can be a single flag or a set of
  40 supported standards if for example the hardware can only distinguish
  41 between 50 and 60 Hz systems. If no signal was detected, then the driver
  42 will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
  43 the set must contain all standards supported by the current video input
  44 or output.
  45
  46 .. note:: Drivers shall *not* switch the video standard
  47    automatically if a new video standard is detected. Instead, drivers
  48    should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
  49    this) and expect that userspace will take action by calling
  50    :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean
  51    different buffer sizes as well, and you cannot change buffer sizes on
  52    the fly. In general, applications that receive the Source Change event
  53    will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video
  54    standard is valid they will have to stop streaming, set the new
  55    standard, allocate new buffers and start streaming again.
  56
  57
  58 Return Value
  59 ============
  60
  61 On success 0 is returned, on error -1 and the ``errno`` variable is set
  62 appropriately. The generic error codes are described at the
  63 :ref:`Generic Error Codes <gen-errors>` chapter.
  64
  65 ENODATA
  66     Standard video timings are not supported for this input or output.