vidioc-g-audioout.rst 3.0 KB
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.. -*- coding: utf-8; mode: rst -*-

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.. _VIDIOC_G_AUDOUT:
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**************************************
ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT
**************************************

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Name
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====
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VIDIOC_G_AUDOUT - VIDIOC_S_AUDOUT - Query or select the current audio output
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Synopsis
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========

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.. c:function:: int ioctl( int fd, VIDIOC_G_AUDOUT, struct v4l2_audioout *argp )
    :name: VIDIOC_G_AUDOUT
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.. c:function:: int ioctl( int fd, VIDIOC_S_AUDOUT, const struct v4l2_audioout *argp )
    :name: VIDIOC_S_AUDOUT
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Arguments
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=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``argp``


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Description
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===========

To query the current audio output applications zero out the ``reserved``
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array of a struct :c:type:`v4l2_audioout` and call the
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``VIDIOC_G_AUDOUT`` ioctl with a pointer to this structure. Drivers fill
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the rest of the structure or return an ``EINVAL`` error code when the device
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has no audio inputs, or none which combine with the current video
output.

Audio outputs have no writable properties. Nevertheless, to select the
current audio output applications can initialize the ``index`` field and
``reserved`` array (which in the future may contain writable properties)
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of a :c:type:`struct v4l2_audioout <v4l2_audioout>` structure and call the
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``VIDIOC_S_AUDOUT`` ioctl. Drivers switch to the requested output or
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return the ``EINVAL`` error code when the index is out of bounds. This is a
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write-only ioctl, it does not return the current audio output attributes
as ``VIDIOC_G_AUDOUT`` does.

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.. note::

   Connectors on a TV card to loop back the received audio signal
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   to a sound card are not audio outputs in this sense.
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.. c:type:: v4l2_audioout
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|

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.. flat-table:: struct v4l2_audioout
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2


    -  .. row 1

       -  __u32

       -  ``index``

       -  Identifies the audio output, set by the driver or application.

    -  .. row 2

       -  __u8

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       -  ``name``\ [32]
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       -  Name of the audio output, a NUL-terminated ASCII string, for
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	  example: "Line Out". This information is intended for the user,
	  preferably the connector label on the device itself.
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    -  .. row 3

       -  __u32

       -  ``capability``

       -  Audio capability flags, none defined yet. Drivers must set this
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	  field to zero.
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    -  .. row 4

       -  __u32

       -  ``mode``

       -  Audio mode, none defined yet. Drivers and applications (on
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	  ``VIDIOC_S_AUDOUT``) must set this field to zero.
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    -  .. row 5

       -  __u32

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       -  ``reserved``\ [2]
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       -  Reserved for future extensions. Drivers and applications must set
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	  the array to zero.
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Return Value
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============

On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.

EINVAL
    No audio outputs combine with the current video output, or the
    number of the selected audio output is out of bounds or it does not
    combine.
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