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