1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
|
.. -*- coding: utf-8; mode: rst -*-
.. _VIDIOC_G_AUDIO:
************************************
ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
************************************
Name
====
VIDIOC_G_AUDIO - VIDIOC_S_AUDIO - Query or select the current audio input and its attributes
Synopsis
========
.. cpp:function:: int ioctl( int fd, int request, struct v4l2_audio *argp )
.. cpp:function:: int ioctl( int fd, int request, const struct v4l2_audio *argp )
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <func-open>`.
``request``
VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
``argp``
Description
===========
To query the current audio input applications zero out the ``reserved``
array of a struct :ref:`v4l2_audio <v4l2-audio>` and call the
:ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` ioctl with a pointer to this structure. Drivers fill
the rest of the structure or return an ``EINVAL`` error code when the device
has no audio inputs, or none which combine with the current video input.
Audio inputs have one writable property, the audio mode. To select the
current audio input *and* change the audio mode, applications initialize
the ``index`` and ``mode`` fields, and the ``reserved`` array of a
:ref:`struct v4l2_audio <v4l2-audio>` structure and call the :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>`
ioctl. Drivers may switch to a different audio mode if the request
cannot be satisfied. However, this is a write-only ioctl, it does not
return the actual new audio mode.
.. _v4l2-audio:
.. flat-table:: struct v4l2_audio
:header-rows: 0
:stub-columns: 0
:widths: 1 1 2
- .. row 1
- __u32
- ``index``
- Identifies the audio input, set by the driver or application.
- .. row 2
- __u8
- ``name``\ \[32\]
- Name of the audio input, a NUL-terminated ASCII string, for
example: "Line In". This information is intended for the user,
preferably the connector label on the device itself.
- .. row 3
- __u32
- ``capability``
- Audio capability flags, see :ref:`audio-capability`.
- .. row 4
- __u32
- ``mode``
- Audio mode flags set by drivers and applications (on
:ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>` ioctl), see :ref:`audio-mode`.
- .. row 5
- __u32
- ``reserved``\ \[2\]
- Reserved for future extensions. Drivers and applications must set
the array to zero.
.. _audio-capability:
.. flat-table:: Audio Capability Flags
:header-rows: 0
:stub-columns: 0
:widths: 3 1 4
- .. row 1
- ``V4L2_AUDCAP_STEREO``
- 0x00001
- This is a stereo input. The flag is intended to automatically
disable stereo recording etc. when the signal is always monaural.
The API provides no means to detect if stereo is *received*,
unless the audio input belongs to a tuner.
- .. row 2
- ``V4L2_AUDCAP_AVL``
- 0x00002
- Automatic Volume Level mode is supported.
.. _audio-mode:
.. flat-table:: Audio Mode Flags
:header-rows: 0
:stub-columns: 0
:widths: 3 1 4
- .. row 1
- ``V4L2_AUDMODE_AVL``
- 0x00001
- AVL mode is on.
Return Value
============
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 inputs combine with the current video input, or the number
of the selected audio input is out of bounds or it does not combine.
|
