ioctl VIDIOC_ENUMAUDOUT &manvol; VIDIOC_ENUMAUDOUT Enumerate audio outputs int ioctl int fd int request struct v4l2_audioout *argp fd &fd; request VIDIOC_ENUMAUDOUT argp To query the attributes of an audio output applications initialize the index field and zero out the reserved array of a &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; when the index is out of bounds. To enumerate all audio outputs applications shall begin at index zero, incrementing by one until the driver returns EINVAL. Note connectors on a TV card to loop back the received audio signal to a sound card are not audio outputs in this sense. See for a description of &v4l2-audioout;. &return-value; EINVAL The number of the audio output is out of bounds, or there are no audio outputs at all and this ioctl is not supported.