2024-09-09 08:52:07 +00:00
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<refentry id="vidioc-g-modulator">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_G_MODULATOR</refname>
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<refname>VIDIOC_S_MODULATOR</refname>
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<refpurpose>Get or set modulator attributes</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_modulator
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>const struct v4l2_modulator
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>To query the attributes of a modulator applications initialize
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the <structfield>index</structfield> field and zero out the
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<structfield>reserved</structfield> array of a &v4l2-modulator; and
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call the <constant>VIDIOC_G_MODULATOR</constant> ioctl with a pointer
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to this structure. Drivers fill the rest of the structure or return an
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&EINVAL; when the index is out of bounds. To enumerate all modulators
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applications shall begin at index zero, incrementing by one until the
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driver returns <errorcode>EINVAL</errorcode>.</para>
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<para>Modulators have two writable properties, an audio
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modulation set and the radio frequency. To change the modulated audio
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subprograms, applications initialize the <structfield>index
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</structfield> and <structfield>txsubchans</structfield> fields and the
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<structfield>reserved</structfield> array and call the
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<constant>VIDIOC_S_MODULATOR</constant> ioctl. Drivers may choose a
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different audio modulation if the request cannot be satisfied. However
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this is a write-only ioctl, it does not return the actual audio
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modulation selected.</para>
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<para>To change the radio frequency the &VIDIOC-S-FREQUENCY; ioctl
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is available.</para>
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<table pgwide="1" frame="none" id="v4l2-modulator">
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<title>struct <structname>v4l2_modulator</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>index</structfield></entry>
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<entry>Identifies the modulator, set by the
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application.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>name</structfield>[32]</entry>
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<entry>Name of the modulator, a NUL-terminated ASCII
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string. This information is intended for the user.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>capability</structfield></entry>
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<entry>Modulator capability flags. No flags are defined
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for this field, the tuner flags in &v4l2-tuner;
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are used accordingly. The audio flags indicate the ability
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to encode audio subprograms. They will <emphasis>not</emphasis>
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change for example with the current video standard.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>rangelow</structfield></entry>
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<entry>The lowest tunable frequency in units of 62.5
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KHz, or if the <structfield>capability</structfield> flag
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<constant>V4L2_TUNER_CAP_LOW</constant> is set, in units of 62.5
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2024-09-09 08:57:42 +00:00
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Hz, or if the <structfield>capability</structfield> flag
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<constant>V4L2_TUNER_CAP_1HZ</constant> is set, in units of 1 Hz.</entry>
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2024-09-09 08:52:07 +00:00
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>rangehigh</structfield></entry>
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<entry>The highest tunable frequency in units of 62.5
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KHz, or if the <structfield>capability</structfield> flag
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<constant>V4L2_TUNER_CAP_LOW</constant> is set, in units of 62.5
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2024-09-09 08:57:42 +00:00
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Hz, or if the <structfield>capability</structfield> flag
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<constant>V4L2_TUNER_CAP_1HZ</constant> is set, in units of 1 Hz.</entry>
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2024-09-09 08:52:07 +00:00
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>txsubchans</structfield></entry>
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<entry>With this field applications can determine how
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audio sub-carriers shall be modulated. It contains a set of flags as
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defined in <xref linkend="modulator-txsubchans" />. Note the tuner
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<structfield>rxsubchans</structfield> flags are reused, but the
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semantics are different. Video output devices are assumed to have an
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analog or PCM audio input with 1-3 channels. The
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<structfield>txsubchans</structfield> flags select one or more
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channels for modulation, together with some audio subprogram
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indicator, for example a stereo pilot tone.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[4]</entry>
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<entry>Reserved for future extensions. Drivers and
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applications must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="modulator-txsubchans">
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<title>Modulator Audio Transmission Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_TUNER_SUB_MONO</constant></entry>
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<entry>0x0001</entry>
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<entry>Modulate channel 1 as mono audio, when the input
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has more channels, a down-mix of channel 1 and 2. This flag does not
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combine with <constant>V4L2_TUNER_SUB_STEREO</constant> or
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<constant>V4L2_TUNER_SUB_LANG1</constant>.</entry>
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</row>
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<row>
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<entry><constant>V4L2_TUNER_SUB_STEREO</constant></entry>
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<entry>0x0002</entry>
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<entry>Modulate channel 1 and 2 as left and right
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channel of a stereo audio signal. When the input has only one channel
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or two channels and <constant>V4L2_TUNER_SUB_SAP</constant> is also
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set, channel 1 is encoded as left and right channel. This flag does
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not combine with <constant>V4L2_TUNER_SUB_MONO</constant> or
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<constant>V4L2_TUNER_SUB_LANG1</constant>. When the driver does not
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support stereo audio it shall fall back to mono.</entry>
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</row>
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<row>
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<entry><constant>V4L2_TUNER_SUB_LANG1</constant></entry>
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<entry>0x0008</entry>
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<entry>Modulate channel 1 and 2 as primary and secondary
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language of a bilingual audio signal. When the input has only one
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channel it is used for both languages. It is not possible to encode
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the primary or secondary language only. This flag does not combine
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with <constant>V4L2_TUNER_SUB_MONO</constant>,
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<constant>V4L2_TUNER_SUB_STEREO</constant> or
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<constant>V4L2_TUNER_SUB_SAP</constant>. If the hardware does not
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support the respective audio matrix, or the current video standard
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does not permit bilingual audio the
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<constant>VIDIOC_S_MODULATOR</constant> ioctl shall return an &EINVAL;
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and the driver shall fall back to mono or stereo mode.</entry>
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</row>
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<row>
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<entry><constant>V4L2_TUNER_SUB_LANG2</constant></entry>
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<entry>0x0004</entry>
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<entry>Same effect as
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<constant>V4L2_TUNER_SUB_SAP</constant>.</entry>
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</row>
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<row>
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<entry><constant>V4L2_TUNER_SUB_SAP</constant></entry>
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<entry>0x0004</entry>
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<entry>When combined with <constant>V4L2_TUNER_SUB_MONO
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</constant> the first channel is encoded as mono audio, the last
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channel as Second Audio Program. When the input has only one channel
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it is used for both audio tracks. When the input has three channels
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the mono track is a down-mix of channel 1 and 2. When combined with
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<constant>V4L2_TUNER_SUB_STEREO</constant> channel 1 and 2 are
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encoded as left and right stereo audio, channel 3 as Second Audio
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Program. When the input has only two channels, the first is encoded as
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left and right channel and the second as SAP. When the input has only
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one channel it is used for all audio tracks. It is not possible to
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encode a Second Audio Program only. This flag must combine with
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<constant>V4L2_TUNER_SUB_MONO</constant> or
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<constant>V4L2_TUNER_SUB_STEREO</constant>. If the hardware does not
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support the respective audio matrix, or the current video standard
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does not permit SAP the <constant>VIDIOC_S_MODULATOR</constant> ioctl
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shall return an &EINVAL; and driver shall fall back to mono or stereo
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mode.</entry>
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</row>
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<row>
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<entry><constant>V4L2_TUNER_SUB_RDS</constant></entry>
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<entry>0x0010</entry>
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<entry>Enable the RDS encoder for a radio FM transmitter.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The &v4l2-modulator;
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<structfield>index</structfield> is out of bounds.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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