VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT — Query or select the current audio output


int ioctl(int  fd,
 int  request,
 struct v4l2_audioout * argp);
int ioctl(int  fd,
 int  request,
 const struct v4l2_audioout * argp);



File descriptor returned by open().





To query the current audio output applications zero out the reserved array of a struct v4l2_audioout and call the VIDIOC_G_AUDOUT 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 output.

Audio outputs have no writable properties. Nevertheless, to select the current audio output applications can initialize the index field and reserved array (which in the future may contain writable properties) of a v4l2_audioout structure and call the VIDIOC_S_AUDOUT ioctl. Drivers switch to the requested output or return the EINVAL error code when the index is out of bounds. This is a write-only ioctl, it does not return the current audio output attributes as VIDIOC_G_AUDOUT does.

Note connectors on a TV card to loop back the received audio signal to a sound card are not audio outputs in this sense.

Table 72. struct v4l2_audioout

__u32indexIdentifies the audio output, set by the driver or application.
__u8name[32]Name of the audio output, a NUL-terminated ASCII string, for example: "Line Out". This information is intended for the user, preferably the connector label on the device itself.
__u32capabilityAudio capability flags, none defined yet. Drivers must set this field to zero.
__u32modeAudio mode, none defined yet. Drivers and applications (on VIDIOC_S_AUDOUT) must set this field to zero.
__u32reserved[2]Reserved for future extensions. Drivers and applications must set the array to zero.

Return Value

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


No audio outputs combine with the current video output, or the number of the selected audio output is out of bounds or it does not combine, or there are no audio outputs at all and the ioctl is not supported.


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