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


int ioctl(int  fd,
 int  request,
 struct v4l2_audio * argp);
int ioctl(int  fd,
 int  request,
 const struct v4l2_audio * argp);



File descriptor returned by open().





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 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.

Table 69. struct v4l2_audio

__u32indexIdentifies the audio input, set by the driver or application.
__u8name[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.
__u32capabilityAudio capability flags, see Table 70, “Audio Capability Flags”.
__u32modeAudio mode flags set by drivers and applications (on VIDIOC_S_AUDIO ioctl), see Table 71, “Audio Mode Flags”.
__u32reserved[2]Reserved for future extensions. Drivers and applications must set the array to zero.

Table 70. Audio Capability Flags

V4L2_AUDCAP_STEREO0x00001This 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_AVL0x00002Automatic Volume Level mode is supported.

Table 71. Audio Mode Flags

V4L2_AUDMODE_AVL0x00001AVL mode is on.

Return Value

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


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, or there are no audio inputs at all and the ioctl is not supported.


I/O is in progress, the input cannot be switched.