101 lines
2.9 KiB
ReStructuredText
101 lines
2.9 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_G_AUDOUT:
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**************************************
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ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT
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**************************************
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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 )
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:name: VIDIOC_G_AUDOUT
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.. c:function:: int ioctl( int fd, VIDIOC_S_AUDOUT, const struct v4l2_audioout *argp )
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:name: VIDIOC_S_AUDOUT
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Description
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===========
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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
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output.
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Audio outputs have no writable properties. Nevertheless, to select the
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current audio output applications can initialize the ``index`` field and
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``reserved`` array (which in the future may contain writable properties)
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of a struct :c:type:`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
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as ``VIDIOC_G_AUDOUT`` does.
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.. note::
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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
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``index``
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- Identifies the audio output, set by the driver or application.
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* - __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,
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preferably the connector label on the device itself.
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* - __u32
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- ``capability``
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- Audio capability flags, none defined yet. Drivers must set this
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field to zero.
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* - __u32
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- ``mode``
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- 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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* - __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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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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No audio outputs combine with the current video output, or the
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number of the selected audio output is out of bounds or it does not
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combine.
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