1 .. -*- coding: utf-8; mode: rst -*-
3 .. _VIDIOC_G_MODULATOR:
5 ********************************************
6 ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
7 ********************************************
12 VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes
18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_modulator *argp )
20 .. cpp:function:: int ioctl( int fd, int request, const struct v4l2_modulator *argp )
27 File descriptor returned by :ref:`open() <func-open>`.
30 VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
38 To query the attributes of a modulator applications initialize the
39 ``index`` field and zero out the ``reserved`` array of a struct
40 :ref:`v4l2_modulator <v4l2-modulator>` and call the
41 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl with a pointer to this structure. Drivers
42 fill the rest of the structure or return an ``EINVAL`` error code when the
43 index is out of bounds. To enumerate all modulators applications shall
44 begin at index zero, incrementing by one until the driver returns
47 Modulators have two writable properties, an audio modulation set and the
48 radio frequency. To change the modulated audio subprograms, applications
49 initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
50 array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
51 different audio modulation if the request cannot be satisfied. However
52 this is a write-only ioctl, it does not return the actual audio
55 :ref:`SDR <sdr>` specific modulator types are ``V4L2_TUNER_SDR`` and
56 ``V4L2_TUNER_RF``. For SDR devices ``txsubchans`` field must be
57 initialized to zero. The term 'modulator' means SDR transmitter in this
60 To change the radio frequency the
61 :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.
64 .. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{3.0cm}|
68 .. flat-table:: struct v4l2_modulator
80 - Identifies the modulator, set by the application.
88 - Name of the modulator, a NUL-terminated ASCII string.
90 This information is intended for the user.
98 - Modulator capability flags. No flags are defined for this field,
99 the tuner flags in struct :ref:`v4l2_tuner <v4l2-tuner>` are
100 used accordingly. The audio flags indicate the ability to encode
101 audio subprograms. They will *not* change for example with the
102 current video standard.
110 - The lowest tunable frequency in units of 62.5 KHz, or if the
111 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
112 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
113 set, in units of 1 Hz.
121 - The highest tunable frequency in units of 62.5 KHz, or if the
122 ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units of
123 62.5 Hz, or if the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is
124 set, in units of 1 Hz.
132 - With this field applications can determine how audio sub-carriers
133 shall be modulated. It contains a set of flags as defined in
134 :ref:`modulator-txsubchans`.
138 The tuner ``rxsubchans`` flags are reused, but the
139 semantics are different. Video output devices
140 are assumed to have an analog or PCM audio input with 1-3
141 channels. The ``txsubchans`` flags select one or more channels
142 for modulation, together with some audio subprogram indicator,
143 for example, a stereo pilot tone.
151 - :cspan:`2` Type of the modulator, see :ref:`v4l2-tuner-type`.
159 - Reserved for future extensions.
161 Drivers and applications must set the array to zero.
165 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
167 .. _modulator-txsubchans:
169 .. flat-table:: Modulator Audio Transmission Flags
177 - ``V4L2_TUNER_SUB_MONO``
181 - Modulate channel 1 as mono audio, when the input has more
182 channels, a down-mix of channel 1 and 2. This flag does not
183 combine with ``V4L2_TUNER_SUB_STEREO`` or
184 ``V4L2_TUNER_SUB_LANG1``.
188 - ``V4L2_TUNER_SUB_STEREO``
192 - Modulate channel 1 and 2 as left and right channel of a stereo
193 audio signal. When the input has only one channel or two channels
194 and ``V4L2_TUNER_SUB_SAP`` is also set, channel 1 is encoded as
195 left and right channel. This flag does not combine with
196 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_LANG1``. When the
197 driver does not support stereo audio it shall fall back to mono.
201 - ``V4L2_TUNER_SUB_LANG1``
205 - Modulate channel 1 and 2 as primary and secondary language of a
206 bilingual audio signal. When the input has only one channel it is
207 used for both languages. It is not possible to encode the primary
208 or secondary language only. This flag does not combine with
209 ``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
210 ``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
211 respective audio matrix, or the current video standard does not
212 permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
213 return an ``EINVAL`` error code and the driver shall fall back to mono
218 - ``V4L2_TUNER_SUB_LANG2``
222 - Same effect as ``V4L2_TUNER_SUB_SAP``.
226 - ``V4L2_TUNER_SUB_SAP``
230 - When combined with ``V4L2_TUNER_SUB_MONO`` the first channel is
231 encoded as mono audio, the last channel as Second Audio Program.
232 When the input has only one channel it is used for both audio
233 tracks. When the input has three channels the mono track is a
234 down-mix of channel 1 and 2. When combined with
235 ``V4L2_TUNER_SUB_STEREO`` channel 1 and 2 are encoded as left and
236 right stereo audio, channel 3 as Second Audio Program. When the
237 input has only two channels, the first is encoded as left and
238 right channel and the second as SAP. When the input has only one
239 channel it is used for all audio tracks. It is not possible to
240 encode a Second Audio Program only. This flag must combine with
241 ``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
242 hardware does not support the respective audio matrix, or the
243 current video standard does not permit SAP the
244 :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an ``EINVAL`` error code and
245 driver shall fall back to mono or stereo mode.
249 - ``V4L2_TUNER_SUB_RDS``
253 - Enable the RDS encoder for a radio FM transmitter.
259 On success 0 is returned, on error -1 and the ``errno`` variable is set
260 appropriately. The generic error codes are described at the
261 :ref:`Generic Error Codes <gen-errors>` chapter.
264 The struct :ref:`v4l2_modulator <v4l2-modulator>` ``index`` is