Video for Linux Two API Specification: Revision 0.24
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# ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER

## Name

VIDIOC_G_TUNER, VIDIOC_S_TUNER -- Get or set tuner attributes

## Synopsis

``int ioctl`(int fd, int request, struct v4l2_tuner *argp);`

``int ioctl`(int fd, int request, const struct v4l2_tuner *argp);`

## Arguments

`fd`

  File descriptor returned by `open()`.

`request`

  VIDIOC_G_TUNER, VIDIOC_S_TUNER

`argp`

## Description

To query the attributes of a tuner applications initialize the `index` field and zero out the `reserved` array of a struct v4l2_tuner and call the `VIDIOC_G_TUNER` ioctl with a pointer to this structure. Drivers fill the rest of the structure or return an EINVAL error code when the index is out of bounds. To enumerate all tuners applications shall begin at index zero, incrementing by one until the driver returns EINVAL.

Tuners have two writable properties, the audio mode and the radio frequency. To change the audio mode, applications initialize the `index`, `audmode` and `reserved` fields and call the `VIDIOC_S_TUNER` ioctl. This will not change the current tuner, which is determined by the current video input. Drivers may choose a different audio mode if the requested mode is invalid or unsupported. Since this is a write-only ioctl, it does not return the actually selected audio mode.

To change the radio frequency the `VIDIOC_S_FREQUENCY` ioctl is available.

Table 1. struct `v4l2_tuner`

__u32 | `index` | Identifies the tuner, set by the application.
__u8 | `name`[32] | Name of the tuner, a NUL-terminated ASCII string. This information is intended for the user.
enum v4l2_tuner_type | `type` | Type of the tuner, see Table 2.
__u32 | `capability` | Tuner capability flags, see Table 3. Audio flags indicate the ability to decode audio subprograms. They will not change, for example with the current video standard. When the structure refers to a radio tuner only the `V4L2_TUNER_CAP_LOW` and `V4L2_TUNER_CAP_STEREO` flags can be set.
__u32 | `rangelow` | The lowest tunable frequency in units of 62.5 kHz, or if the `capability` flag `V4L2_TUNER_CAP_LOW` is set, in units of 62.5 Hz.
__u32 | `rangehigh` | The highest tunable frequency in units of 62.5 kHz, or if the `capability` flag `V4L2_TUNER_CAP_LOW` is set, in units of 62.5 Hz.
__u32 | `rxsubchans` | Some tuners or audio decoders can determine the received audio subprograms by analyzing audio carriers, pilot tones or other indicators. To pass this information drivers set flags defined in Table 4 in this field. For example:
|  | `V4L2_TUNER_SUB_MONO` | receiving mono audio
|  | `STEREO | SAP` | receiving stereo audio and a secondary audio program
|  | `MONO | STEREO` | receiving mono or stereo audio, the hardware cannot distinguish
|  | `LANG1 | LANG2` | receiving bilingual audio
|  | `MONO | STEREO | LANG1 | LANG2` | receiving mono, stereo or bilingual audio
|  | When the `V4L2_TUNER_CAP_STEREO`, `_LANG1`, `_LANG2` or `_SAP` flag is cleared in the `capability` field, the corresponding `V4L2_TUNER_SUB_` flag must not be set here. This field is valid only if this is the tuner of the current video input, or when the structure refers to a radio tuner.
__u32 | `audmode` | The selected audio mode, see Table 5 for valid values. The audio mode does not affect audio subprogram detection, and like a control it does not automatically change unless the requested mode is invalid or unsupported. See Table 6 for possible results when the selected and received audio programs do not match. Currently this is the only field of struct `v4l2_tuner` applications can change.
__u32 | `signal` | The signal strength if known, ranging from 0 to 65535. Higher values indicate a better signal.
__s32 | `afc` | Automatic frequency control: When the `afc` value is negative, the frequency is too low, when positive too high.
__u32 | `reserved`[4] | Reserved for future extensions. Drivers and applications must set the array to zero.

Table 2. enum v4l2_tuner_type

`V4L2_TUNER_RADIO` | 1 |
`V4L2_TUNER_ANALOG_TV` | 2 |

Table 3. Tuner and Modulator Capability Flags

`V4L2_TUNER_CAP_LOW` | 0x0001 | When set, tuning frequencies are expressed in units of 62.5 Hz, otherwise in units of 62.5 kHz.
`V4L2_TUNER_CAP_NORM` | 0x0002 | This is a multi-standard tuner; the video standard can or must be switched. (B/G PAL tuners for example are typically not considered multi-standard because the video standard is automatically determined from the frequency band.) The set of supported video standards is available from the struct v4l2_input pointing to this tuner, see the description of ioctl `VIDIOC_ENUMINPUT` for details. Only `V4L2_TUNER_ANALOG_TV` tuners can have this capability.
`V4L2_TUNER_CAP_STEREO` | 0x0010 | Stereo audio reception is supported.
`V4L2_TUNER_CAP_LANG1` | 0x0040 | Reception of the primary language of a bilingual audio program is supported. Bilingual audio is a feature of two-channel systems, transmitting the primary language monaural on the main audio carrier and a secondary language monaural on a second carrier. Only `V4L2_TUNER_ANALOG_TV` tuners can have this capability.
`V4L2_TUNER_CAP_LANG2` | 0x0020 | Reception of the secondary language of a bilingual audio program is supported. Only `V4L2_TUNER_ANALOG_TV` tuners can have this capability.
`V4L2_TUNER_CAP_SAP` | 0x0020 | Reception of a secondary audio program is supported. This is a feature of the BTSC system which accompanies the NTSC video standard. Two audio carriers are available for mono or stereo transmissions of a primary language, and an independent third carrier for a monaural secondary language. Only `V4L2_TUNER_ANALOG_TV` tuners can have this capability. Note the `V4L2_TUNER_CAP_LANG2` and `V4L2_TUNER_CAP_SAP` flags are synonyms. `V4L2_TUNER_CAP_SAP` applies when the tuner supports the `V4L2_STD_NTSC_M` video standard.

Table 4. Tuner Audio Reception Flags

`V4L2_TUNER_SUB_MONO` | 0x0001 | The tuner receives a mono audio signal.
`V4L2_TUNER_SUB_STEREO` | 0x0002 | The tuner receives a stereo audio signal.
`V4L2_TUNER_SUB_LANG1` | 0x0008 | The tuner receives the primary language of a bilingual audio signal. Drivers must clear this flag when the current video standard is `V4L2_STD_NTSC_M`.
`V4L2_TUNER_SUB_LANG2` | 0x0004 | The tuner receives the secondary language of a bilingual audio signal (or a second audio program).
`V4L2_TUNER_SUB_SAP` | 0x0004 | The tuner receives a Second Audio Program. Note the `V4L2_TUNER_SUB_LANG2` and `V4L2_TUNER_SUB_SAP` flags are synonyms. The `V4L2_TUNER_SUB_SAP` flag applies when the current video standard is `V4L2_STD_NTSC_M`.

Table 5. Tuner Audio Modes

`V4L2_TUNER_MODE_MONO` | 0 | Play mono audio. When the tuner receives a stereo signal this a down-mix of the left and right channel. When the tuner receives a bilingual or SAP signal this mode selects the primary language.
`V4L2_TUNER_MODE_STEREO` | 1 | Play stereo audio. When the tuner receives bilingual audio it may play different languages on the left and right channel or the primary language on both channels. behave as in mono mode. Playing different languages in this mode is deprecated. New drivers should do this only in `MODE_LANG1_LANG2`. When the tuner receives no stereo signal or does not support stereo reception the driver shall fall back to `MODE_MONO`.
`V4L2_TUNER_MODE_LANG1` | 3 | Play the primary language, mono or stereo. Only `V4L2_TUNER_ANALOG_TV` tuners support this mode.
`V4L2_TUNER_MODE_LANG2` | 2 | Play the secondary language, mono. When the tuner receives no bilingual audio or SAP, or their reception is not supported the driver shall fall back to mono or stereo mode. Only `V4L2_TUNER_ANALOG_TV` tuners support this mode.
`V4L2_TUNER_MODE_SAP` | 2 | Play the Second Audio Program. When the tuner receives no bilingual audio or SAP, or their reception is not supported the driver shall fall back to mono or stereo mode. Only `V4L2_TUNER_ANALOG_TV` tuners support this mode. Note the `V4L2_TUNER_MODE_LANG2` and `V4L2_TUNER_MODE_SAP` are synonyms.
`V4L2_TUNER_MODE_LANG1_LANG2` | 4 | Play the primary language on the left channel, the secondary language on the right channel. When the tuner receives no bilingual audio or SAP, it shall fall back to `MODE_LANG1` or `MODE_MONO`. Only `V4L2_TUNER_ANALOG_TV` tuners support this mode.

Table 6. Tuner Audio Matrix

| Selected `V4L2_TUNER_MODE_`
--- | ---
Received `V4L2_TUNER_SUB_` | `MONO` | `STEREO` | `LANG1` | `LANG2 = SAP` | `LANG1_LANG2`[a]
`MONO` | Mono | Mono/Mono | Mono | Mono | Mono/Mono
`MONO | SAP` | Mono | Mono/Mono | Mono | SAP | Mono/SAP (preferred) or Mono/Mono
`STEREO` | L+R | L/R | Stereo L/R (preferred) or Mono L+R | Stereo L/R (preferred) or Mono L+R | L/R (preferred) or L+R/L+R
`STEREO | SAP` | L+R | L/R | Stereo L/R (preferred) or Mono L+R | SAP | L+R/SAP (preferred) or L/R or L+R/L+R
`LANG1 | LANG2` | Language 1 | Lang1/Lang2 (deprecated[b]) or Lang1/Lang1 | Language 1 | Language 2 | Lang1/Lang2 (preferred) or Lang1/Lang1
Notes: a. This mode has been added in Linux 2.6.17 and may not be supported by older drivers. b. Playback of both languages in `MODE_STEREO` is deprecated. In the future drivers should produce only the primary language in this mode. Applications should request `MODE_LANG1_LANG2` to record both languages or a stereo signal.

## Return Value

On success 0 is returned, on error -1 and the `errno` variable is set appropriately:

EINVAL

  The struct v4l2_tuner `index` is out of bounds.

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