Provided by: oss4-base_4.2-build2004-1ubuntu2_i386
oss_audioloop - Loopback audio driver.
The loopback audio driver makes it possible to create special purpose
virtual audio devices based on user land server processes.
Loopback devices are driven by a timer interrupt and no real audio
hardware is required.
Audio loopback devices are like named pipes or pseudo terminals. They
are grouped in client and server device pairs. The server side device
must be open before the client side device can be opened.
Loopback devices are typically used to implement server based special
purpose audio devices. This kind of server can for example transfer the
audio data played by the client application to some remote system using
some VoIP protocol. However the server application doesn't need to be
any dedicated server. Practically any audio application can be used as
SERVER SIDE DEVICE
The server side applications sets up the native sampling rate and
sample format (number of bits and channels). The server side device can
be opened for input (O_RDONLY) pr output (O_WRONLY). Opening for
simultaneous input and output (O_RDWR) is not permitted.
The server application will automatically be paused at the moment it
tries to read or write audio data for the first time. It will be kept
in sleep until the client side application starts writing or reading
data. This sleep period may last forever and in some cases the first
write/read call never returns. For this reason it's not recommended to
use GUI based audio applications as the server. Note that this wait
will occur even in the non-blocking (O_NONBLOCK) mode (this is
intentional feature and not a bug).
CLIENT SIDE DEVICE
The client side device is typically used by any ordinary audio
application. There is nothing special in loopback devices.
Since the loop is unidirectional the client side will be forced to be
write only if the server side device is open for recording and vice
The loop will use the sample rate and sample format (number of bits and
channels) set by the server side application. If the client uses
different settings then OSS will perform the required sampling rate and
format conversions automatically.
Audio loopback devices differ from "normal" audio devices because an
application is needed at the both ends of the loop. The loop device
will return a "Connection reset by peer" error (ECONNRESET) error.
Applications designed to be used as loopback based server applications
can/should use this error (returned by read or write) as an end-of-
Specifies how many loopback client/server audio device pairs to
o There is no mixer (volume control) related with loopback audio
devices. This may prevent poorly designed audio applications (that
expect/require a mixer) from working. There is no workaround
o The server side application will wait until the client side
application starts using it. This wait may last forever which in
turn may cause unrecoverable (network) problems with some
o Loopback devices may return "Connection reset by peer" error when
the reote side of the loop disconnects the device. Some recording
applications may fail to save the recorded data properly because of
this. Use some other application (such as ossrecord) if this
/etc/oss4/conf/oss_audioloop.conf Device configuration file
27 September 2011 oss_audioloop(7)