ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR &manvol; VIDIOC_G_MODULATOR VIDIOC_S_MODULATOR Get or set modulator attributes int ioctl int fd int request struct v4l2_modulator *argp int ioctl int fd int request const struct v4l2_modulator *argp fd &fd; request VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR argp To query the attributes of a modulator applications initialize the index field and zero out the reserved array of a &v4l2-modulator; and call the VIDIOC_G_MODULATOR ioctl with a pointer to this structure. Drivers fill the rest of the structure or return an &EINVAL; when the index is out of bounds. To enumerate all modulators applications shall begin at index zero, incrementing by one until the driver returns EINVAL. Modulators have two writable properties, an audio modulation set and the radio frequency. To change the modulated audio subprograms, applications initialize the index and txsubchans fields and the reserved array and call the VIDIOC_S_MODULATOR ioctl. Drivers may choose a different audio modulation if the request cannot be satisfied. However this is a write-only ioctl, it does not return the actual audio modulation selected. SDR specific modulator types are V4L2_TUNER_SDR and V4L2_TUNER_RF. For SDR devices txsubchans field must be initialized to zero. The term 'modulator' means SDR transmitter in this context. To change the radio frequency the &VIDIOC-S-FREQUENCY; ioctl is available. &cs-str; __u32 index Identifies the modulator, set by the application. __u8 name[32] Name of the modulator, a NUL-terminated ASCII string. This information is intended for the user. __u32 capability Modulator capability flags. No flags are defined for this field, the tuner flags in &v4l2-tuner; are used accordingly. The audio flags indicate the ability to encode audio subprograms. They will not change for example with the current video standard. __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, or if the capability flag V4L2_TUNER_CAP_1HZ is set, in units of 1 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, or if the capability flag V4L2_TUNER_CAP_1HZ is set, in units of 1 Hz. __u32 txsubchans With this field applications can determine how audio sub-carriers shall be modulated. It contains a set of flags as defined in . Note the tuner rxsubchans flags are reused, but the semantics are different. Video output devices are assumed to have an analog or PCM audio input with 1-3 channels. The txsubchans flags select one or more channels for modulation, together with some audio subprogram indicator, for example a stereo pilot tone. __u32 type Type of the modulator, see . __u32 reserved[3] Reserved for future extensions. Drivers and applications must set the array to zero. &cs-def; V4L2_TUNER_SUB_MONO 0x0001 Modulate channel 1 as mono audio, when the input has more channels, a down-mix of channel 1 and 2. This flag does not combine with V4L2_TUNER_SUB_STEREO or V4L2_TUNER_SUB_LANG1. V4L2_TUNER_SUB_STEREO 0x0002 Modulate channel 1 and 2 as left and right channel of a stereo audio signal. When the input has only one channel or two channels and V4L2_TUNER_SUB_SAP is also set, channel 1 is encoded as left and right channel. This flag does not combine with V4L2_TUNER_SUB_MONO or V4L2_TUNER_SUB_LANG1. When the driver does not support stereo audio it shall fall back to mono. V4L2_TUNER_SUB_LANG1 0x0008 Modulate channel 1 and 2 as primary and secondary language of a bilingual audio signal. When the input has only one channel it is used for both languages. It is not possible to encode the primary or secondary language only. This flag does not combine with V4L2_TUNER_SUB_MONO, V4L2_TUNER_SUB_STEREO or V4L2_TUNER_SUB_SAP. If the hardware does not support the respective audio matrix, or the current video standard does not permit bilingual audio the VIDIOC_S_MODULATOR ioctl shall return an &EINVAL; and the driver shall fall back to mono or stereo mode. V4L2_TUNER_SUB_LANG2 0x0004 Same effect as V4L2_TUNER_SUB_SAP. V4L2_TUNER_SUB_SAP 0x0004 When combined with V4L2_TUNER_SUB_MONO the first channel is encoded as mono audio, the last channel as Second Audio Program. When the input has only one channel it is used for both audio tracks. When the input has three channels the mono track is a down-mix of channel 1 and 2. When combined with V4L2_TUNER_SUB_STEREO channel 1 and 2 are encoded as left and right stereo audio, channel 3 as Second Audio Program. When the input has only two channels, the first is encoded as left and right channel and the second as SAP. When the input has only one channel it is used for all audio tracks. It is not possible to encode a Second Audio Program only. This flag must combine with V4L2_TUNER_SUB_MONO or V4L2_TUNER_SUB_STEREO. If the hardware does not support the respective audio matrix, or the current video standard does not permit SAP the VIDIOC_S_MODULATOR ioctl shall return an &EINVAL; and driver shall fall back to mono or stereo mode. V4L2_TUNER_SUB_RDS 0x0010 Enable the RDS encoder for a radio FM transmitter. &return-value; EINVAL The &v4l2-modulator; index is out of bounds.