1 .. -*- coding: utf-8; mode: rst -*-
3 .. _VIDIOC_G_MODULATOR:
5 ********************************************
6 ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
7 ********************************************
9 *man VIDIOC_G_MODULATOR(2)*
12 Get or set modulator attributes
18 .. c:function:: int ioctl( int fd, int request, struct v4l2_modulator *argp )
20 .. c:function:: int ioctl( int fd, int request, const struct v4l2_modulator *argp )
26 File descriptor returned by :ref:`open() <func-open>`.
29 VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
37 To query the attributes of a modulator applications initialize the
38 ``index`` field and zero out the ``reserved`` array of a struct
39 :ref:`v4l2_modulator <v4l2-modulator>` and call the
40 ``VIDIOC_G_MODULATOR`` ioctl with a pointer to this structure. Drivers
41 fill the rest of the structure or return an EINVAL error code when the
42 index is out of bounds. To enumerate all modulators applications shall
43 begin at index zero, incrementing by one until the driver returns
46 Modulators have two writable properties, an audio modulation set and the
47 radio frequency. To change the modulated audio subprograms, applications
48 initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
49 array and call the ``VIDIOC_S_MODULATOR`` ioctl. Drivers may choose a
50 different audio modulation if the request cannot be satisfied. However
51 this is a write-only ioctl, it does not return the actual audio
54 :ref:`SDR <sdr>` specific modulator types are ``V4L2_TUNER_SDR`` and
55 ``V4L2_TUNER_RF``. For SDR devices ``txsubchans`` field must be
56 initialized to zero. The term 'modulator' means SDR transmitter in this
59 To change the radio frequency the
60 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
65 .. flat-table:: struct v4l2_modulator
77 - Identifies the modulator, set by the application.
85 - Name of the modulator, a NUL-terminated ASCII string. This
86 information is intended for the user.
94 - Modulator capability flags. No flags are defined for this field,
95 the tuner flags in struct :ref:`v4l2_tuner <v4l2-tuner>` are
96 used accordingly. The audio flags indicate the ability to encode
97 audio subprograms. They will *not* change for example with the
98 current video standard.
106 - The lowest tunable frequency in units of 62.5 KHz, or if the
107 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
108 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
109 set, in units of 1 Hz.
117 - The highest tunable frequency in units of 62.5 KHz, or if the
118 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
119 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
120 set, in units of 1 Hz.
128 - With this field applications can determine how audio sub-carriers
129 shall be modulated. It contains a set of flags as defined in
130 :ref:`modulator-txsubchans`. Note the tuner ``rxsubchans`` flags
131 are reused, but the semantics are different. Video output devices
132 are assumed to have an analog or PCM audio input with 1-3
133 channels. The ``txsubchans`` flags select one or more channels for
134 modulation, together with some audio subprogram indicator, for
135 example a stereo pilot tone.
143 - :cspan:`2` Type of the modulator, see :ref:`v4l2-tuner-type`.
151 - Reserved for future extensions. Drivers and applications must set
156 .. _modulator-txsubchans:
158 .. flat-table:: Modulator Audio Transmission Flags
166 - ``V4L2_TUNER_SUB_MONO``
170 - Modulate channel 1 as mono audio, when the input has more
171 channels, a down-mix of channel 1 and 2. This flag does not
172 combine with ``V4L2_TUNER_SUB_STEREO`` or
173 ``V4L2_TUNER_SUB_LANG1``.
177 - ``V4L2_TUNER_SUB_STEREO``
181 - Modulate channel 1 and 2 as left and right channel of a stereo
182 audio signal. When the input has only one channel or two channels
183 and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
184 left and right channel. This flag does not combine with
185 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
186 driver does not support stereo audio it shall fall back to mono.
190 - ``V4L2_TUNER_SUB_LANG1``
194 - Modulate channel 1 and 2 as primary and secondary language of a
195 bilingual audio signal. When the input has only one channel it is
196 used for both languages. It is not possible to encode the primary
197 or secondary language only. This flag does not combine with
198 ``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
199 ``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
200 respective audio matrix, or the current video standard does not
201 permit bilingual audio the ``VIDIOC_S_MODULATOR`` ioctl shall
202 return an EINVAL error code and the driver shall fall back to mono
207 - ``V4L2_TUNER_SUB_LANG2``
211 - Same effect as ``V4L2_TUNER_SUB_SAP``.
215 - ``V4L2_TUNER_SUB_SAP``
219 - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
220 encoded as mono audio, the last channel as Second Audio Program.
221 When the input has only one channel it is used for both audio
222 tracks. When the input has three channels the mono track is a
223 down-mix of channel 1 and 2. When combined with
224 ``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
225 right stereo audio, channel 3 as Second Audio Program. When the
226 input has only two channels, the first is encoded as left and
227 right channel and the second as SAP. When the input has only one
228 channel it is used for all audio tracks. It is not possible to
229 encode a Second Audio Program only. This flag must combine with
230 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
231 hardware does not support the respective audio matrix, or the
232 current video standard does not permit SAP the
233 ``VIDIOC_S_MODULATOR`` ioctl shall return an EINVAL error code and
234 driver shall fall back to mono or stereo mode.
238 - ``V4L2_TUNER_SUB_RDS``
242 - Enable the RDS encoder for a radio FM transmitter.
249 On success 0 is returned, on error -1 and the ``errno`` variable is set
250 appropriately. The generic error codes are described at the
251 :ref:`Generic Error Codes <gen-errors>` chapter.
254 The struct :ref:`v4l2_modulator <v4l2-modulator>` ``index`` is
258 .. ------------------------------------------------------------------------------
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264 .. ------------------------------------------------------------------------------