Video for Linux Two API Specification: Revision 0.24
PrevNext

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

__u32indexIdentifies the tuner, set by the application.
__u8name[32]

Name of the tuner, a NUL-terminated ASCII string. This information is intended for the user.

enum v4l2_tuner_typetypeType of the tuner, see Table 2.
__u32capability

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.

__u32rangelowThe 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.
__u32rangehighThe 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.
__u32rxsubchans

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_MONOreceiving mono audio
  STEREO | SAPreceiving stereo audio and a secondary audio program
  MONO | STEREOreceiving mono or stereo audio, the hardware cannot distinguish
  LANG1 | LANG2receiving bilingual audio
  MONO | STEREO | LANG1 | LANG2receiving 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.

__u32audmode

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.

__u32signalThe signal strength if known, ranging from 0 to 65535. Higher values indicate a better signal.
__s32afcAutomatic frequency control: When the afc value is negative, the frequency is too low, when positive too high.
__u32reserved[4]Reserved for future extensions. Drivers and applications must set the array to zero.

Table 2. enum v4l2_tuner_type

V4L2_TUNER_RADIO1 
V4L2_TUNER_ANALOG_TV2 

Table 3. Tuner and Modulator Capability Flags

V4L2_TUNER_CAP_LOW0x0001When set, tuning frequencies are expressed in units of 62.5 Hz, otherwise in units of 62.5 kHz.
V4L2_TUNER_CAP_NORM0x0002This 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_STEREO0x0010Stereo audio reception is supported.
V4L2_TUNER_CAP_LANG10x0040Reception 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_LANG20x0020Reception of the secondary language of a bilingual audio program is supported. Only V4L2_TUNER_ANALOG_TV tuners can have this capability.
V4L2_TUNER_CAP_SAP0x0020

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_MONO0x0001The tuner receives a mono audio signal.
V4L2_TUNER_SUB_STEREO0x0002The tuner receives a stereo audio signal.
V4L2_TUNER_SUB_LANG10x0008The 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_LANG20x0004The tuner receives the secondary language of a bilingual audio signal (or a second audio program).
V4L2_TUNER_SUB_SAP0x0004The 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_MONO0Play 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_STEREO1

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_LANG13Play the primary language, mono or stereo. Only V4L2_TUNER_ANALOG_TV tuners support this mode.
V4L2_TUNER_MODE_LANG22Play 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_SAP2Play 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_LANG24Play 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_MONOSTEREOLANG1LANG2 = SAPLANG1_LANG2[a]
MONOMonoMono/MonoMonoMonoMono/Mono
MONO | SAPMonoMono/MonoMonoSAPMono/SAP (preferred) or Mono/Mono
STEREOL+RL/RStereo L/R (preferred) or Mono L+RStereo L/R (preferred) or Mono L+RL/R (preferred) or L+R/L+R
STEREO | SAPL+RL/RStereo L/R (preferred) or Mono L+RSAPL+R/SAP (preferred) or L/R or L+R/L+R
LANG1 | LANG2Language 1Lang1/Lang2 (deprecated[b]) or Lang1/Lang1Language 1Language 2Lang1/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.

PrevHomeNext
ioctl VIDIOC_G_STD, VIDIOC_S_STDUpioctl VIDIOC_LOG_STATUS