File descriptor returned by
To query the attributes of an audio input applications
index field and zero out the
reserved array of a struct v4l2_audio
and call the
VIDIOC_ENUMAUDIO ioctl with a pointer
to this structure. Drivers fill the rest of the structure or return an
EINVAL error code when the index is out of bounds. To enumerate all audio
inputs applications shall begin at index zero, incrementing by one
until the driver returns EINVAL.
On success 0 is returned, on error -1 and the
errno variable is set appropriately:
The number of the audio input is out of bounds, or there are no audio inputs at all and this ioctl is not supported.