7.22.1. Name

VIDIOC_G_AUDIO - VIDIOC_S_AUDIO - Query or select the current audio input and its attributes

7.22.2. Synopsis

int ioctl(int fd, VIDIOC_G_AUDIO, struct v4l2_audio *argp)
int ioctl(int fd, VIDIOC_S_AUDIO, const struct v4l2_audio *argp)

7.22.3. Arguments

File descriptor returned by open().
Pointer to struct v4l2_audio.

7.22.4. Description

To query the current audio input applications zero out the reserved array of a struct v4l2_audio and call the VIDIOC_G_AUDIO ioctl with a pointer to this structure. Drivers fill the rest of the structure or return an EINVAL error code when the device has no audio inputs, or none which combine with the current video input.

Audio inputs have one writable property, the audio mode. To select the current audio input and change the audio mode, applications initialize the index and mode fields, and the reserved array of a struct v4l2_audio structure and call the VIDIOC_S_AUDIO ioctl. Drivers may switch to a different audio mode if the request cannot be satisfied. However, this is a write-only ioctl, it does not return the actual new audio mode.

struct v4l2_audio
__u32 index Identifies the audio input, set by the driver or application.
__u8 name[32] Name of the audio input, a NUL-terminated ASCII string, for example: “Line In”. This information is intended for the user, preferably the connector label on the device itself.
__u32 capability Audio capability flags, see Audio Capability Flags.
__u32 mode Audio mode flags set by drivers and applications (on VIDIOC_S_AUDIO ioctl), see Audio Mode Flags.
__u32 reserved[2] Reserved for future extensions. Drivers and applications must set the array to zero.
Audio Capability Flags
V4L2_AUDCAP_STEREO 0x00001 This is a stereo input. The flag is intended to automatically disable stereo recording etc. when the signal is always monaural. The API provides no means to detect if stereo is received, unless the audio input belongs to a tuner.
V4L2_AUDCAP_AVL 0x00002 Automatic Volume Level mode is supported.
Audio Mode Flags
V4L2_AUDMODE_AVL 0x00001 AVL mode is on.

7.22.5. Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

No audio inputs combine with the current video input, or the number of the selected audio input is out of bounds or it does not combine.