129 lines
3.5 KiB
ReStructuredText
Executable file
129 lines
3.5 KiB
ReStructuredText
Executable file
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_G_AUDIO:
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************************************
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ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
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************************************
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Name
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====
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VIDIOC_G_AUDIO - VIDIOC_S_AUDIO - Query or select the current audio input and its attributes
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_G_AUDIO, struct v4l2_audio *argp )
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:name: VIDIOC_G_AUDIO
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.. c:function:: int ioctl( int fd, VIDIOC_S_AUDIO, const struct v4l2_audio *argp )
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:name: VIDIOC_S_AUDIO
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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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Pointer to struct :c:type:`v4l2_audio`.
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Description
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===========
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To query the current audio input applications zero out the ``reserved``
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array of a struct :c:type:`v4l2_audio` and call the
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:ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` 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 input.
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Audio inputs have one writable property, the audio mode. To select the
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current audio input *and* change the audio mode, applications initialize
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the ``index`` and ``mode`` fields, and the ``reserved`` array of a
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struct :c:type:`v4l2_audio` structure and call the :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>`
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ioctl. Drivers may switch to a different audio mode if the request
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cannot be satisfied. However, this is a write-only ioctl, it does not
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return the actual new audio mode.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. c:type:: v4l2_audio
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.. flat-table:: struct v4l2_audio
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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 input, 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 input, a NUL-terminated ASCII string, for
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example: "Line In". 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, see :ref:`audio-capability`.
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* - __u32
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- ``mode``
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- Audio mode flags set by drivers and applications (on
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:ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>` ioctl), see :ref:`audio-mode`.
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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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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _audio-capability:
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.. flat-table:: Audio Capability Flags
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_AUDCAP_STEREO``
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- 0x00001
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- This is a stereo input. The flag is intended to automatically
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disable stereo recording etc. when the signal is always monaural.
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The API provides no means to detect if stereo is *received*,
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unless the audio input belongs to a tuner.
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* - ``V4L2_AUDCAP_AVL``
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- 0x00002
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- Automatic Volume Level mode is supported.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _audio-mode:
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.. flat-table:: Audio Mode Flags
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_AUDMODE_AVL``
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- 0x00001
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- AVL mode is on.
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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 inputs combine with the current video input, or the number
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of the selected audio input is out of bounds or it does not combine.
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