vidioc-g-audio.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _VIDIOC_G_AUDIO:
  5
  6************************************
  7ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
  8************************************
  9
 10Name
 11====
 12
 13VIDIOC_G_AUDIO - VIDIOC_S_AUDIO - Query or select the current audio input and its attributes
 14
 15Synopsis
 16========
 17
 18.. c:macro:: VIDIOC_G_AUDIO
 19
 20``int ioctl(int fd, VIDIOC_G_AUDIO, struct v4l2_audio *argp)``
 21
 22.. c:macro:: VIDIOC_S_AUDIO
 23
 24``int ioctl(int fd, VIDIOC_S_AUDIO, const struct v4l2_audio *argp)``
 25
 26Arguments
 27=========
 28
 29``fd``
 30    File descriptor returned by :c:func:`open()`.
 31
 32``argp``
 33    Pointer to struct :c:type:`v4l2_audio`.
 34
 35Description
 36===========
 37
 38To query the current audio input applications zero out the ``reserved``
 39array of a struct :c:type:`v4l2_audio` and call the
 40:ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` ioctl with a pointer to this structure. Drivers fill
 41the rest of the structure or return an ``EINVAL`` error code when the device
 42has no audio inputs, or none which combine with the current video input.
 43
 44Audio inputs have one writable property, the audio mode. To select the
 45current audio input *and* change the audio mode, applications initialize
 46the ``index`` and ``mode`` fields, and the ``reserved`` array of a
 47struct :c:type:`v4l2_audio` structure and call the :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>`
 48ioctl. Drivers may switch to a different audio mode if the request
 49cannot be satisfied. However, this is a write-only ioctl, it does not
 50return the actual new audio mode.
 51
 52.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
 53
 54.. c:type:: v4l2_audio
 55
 56.. flat-table:: struct v4l2_audio
 57    :header-rows:  0
 58    :stub-columns: 0
 59    :widths:       1 1 2
 60
 61    * - __u32
 62      - ``index``
 63      - Identifies the audio input, set by the driver or application.
 64    * - __u8
 65      - ``name``\ [32]
 66      - Name of the audio input, a NUL-terminated ASCII string, for
 67	example: "Line In". This information is intended for the user,
 68	preferably the connector label on the device itself.
 69    * - __u32
 70      - ``capability``
 71      - Audio capability flags, see :ref:`audio-capability`.
 72    * - __u32
 73      - ``mode``
 74      - Audio mode flags set by drivers and applications (on
 75	:ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>` ioctl), see :ref:`audio-mode`.
 76    * - __u32
 77      - ``reserved``\ [2]
 78      - Reserved for future extensions. Drivers and applications must set
 79	the array to zero.
 80
 81
 82.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
 83
 84.. _audio-capability:
 85
 86.. flat-table:: Audio Capability Flags
 87    :header-rows:  0
 88    :stub-columns: 0
 89    :widths:       3 1 4
 90
 91    * - ``V4L2_AUDCAP_STEREO``
 92      - 0x00001
 93      - This is a stereo input. The flag is intended to automatically
 94	disable stereo recording etc. when the signal is always monaural.
 95	The API provides no means to detect if stereo is *received*,
 96	unless the audio input belongs to a tuner.
 97    * - ``V4L2_AUDCAP_AVL``
 98      - 0x00002
 99      - Automatic Volume Level mode is supported.
100
101
102.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
103
104.. _audio-mode:
105
106.. flat-table:: Audio Mode Flags
107    :header-rows:  0
108    :stub-columns: 0
109    :widths:       3 1 4
110
111    * - ``V4L2_AUDMODE_AVL``
112      - 0x00001
113      - AVL mode is on.
114
115Return Value
116============
117
118On success 0 is returned, on error -1 and the ``errno`` variable is set
119appropriately. The generic error codes are described at the
120:ref:`Generic Error Codes <gen-errors>` chapter.
121
122EINVAL
123    No audio inputs combine with the current video input, or the number
124    of the selected audio input is out of bounds or it does not combine.