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 *man VIDIOC_QUERYSTD(2)*
  10
  11 Sense the video standard received by the current input
  12
  13
  14 Synopsis
  15 ========
  16
  17 .. c:function:: int ioctl( int fd, int request, v4l2_std_id *argp )
  18
  19 Arguments
  20 =========
  21
  22 ``fd``
  23     File descriptor returned by :ref:`open() <func-open>`.
  24
  25 ``request``
  26     VIDIOC_QUERYSTD
  27
  28 ``argp``
  29
  30
  31 Description
  32 ===========
  33
  34 The hardware may be able to detect the current video standard
  35 automatically. To do so, applications call ``VIDIOC_QUERYSTD`` with a
  36 pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
  37 stores here a set of candidates, this can be a single flag or a set of
  38 supported standards if for example the hardware can only distinguish
  39 between 50 and 60 Hz systems. If no signal was detected, then the driver
  40 will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
  41 the set must contain all standards supported by the current video input
  42 or output.
  43
  44 Please note that drivers shall *not* switch the video standard
  45 automatically if a new video standard is detected. Instead, drivers
  46 should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
  47 this) and expect that userspace will take action by calling
  48 ``VIDIOC_QUERYSTD``. The reason is that a new video standard can mean
  49 different buffer sizes as well, and you cannot change buffer sizes on
  50 the fly. In general, applications that receive the Source Change event
  51 will have to call ``VIDIOC_QUERYSTD``, and if the detected video
  52 standard is valid they will have to stop streaming, set the new
  53 standard, allocate new buffers and start streaming again.
  54
  55
  56 Return Value
  57 ============
  58
  59 On success 0 is returned, on error -1 and the ``errno`` variable is set
  60 appropriately. The generic error codes are described at the
  61 :ref:`Generic Error Codes <gen-errors>` chapter.
  62
  63 ENODATA
  64     Standard video timings are not supported for this input or output.
  65
  66
  67 .. ------------------------------------------------------------------------------
  68 .. This file was automatically converted from DocBook-XML with the dbxml
  69 .. library (https://github.com/return42/sphkerneldoc). The origin XML comes
  70 .. from the linux kernel, refer to:
  71 ..
  72 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
  73 .. ------------------------------------------------------------------------------