Ubuntu Manpage: bluealsa-plugins - Bluetooth Audio ALSA Plugins

Provided by: libasound2-plugin-bluez_4.0.0-2_amd64

NAME

       bluealsa-plugins - Bluetooth Audio ALSA Plugins

SYNOPSIS

       BlueALSA  permits  applications  to access Bluetooth audio devices using the ALSA alsa-lib
       API. Users of those applications can then use Bluetooth speakers, headphones, headsets and
       hands-free devices much as if they were local devices. This integration is achieved by two
       ALSA plugins, one for PCM audio streams and one for CTL volume controls.

PCM PLUGIN

The BlueALSA ALSA PCM plugin communicates with the bluealsa(8) service. It can be used to
define ALSA PCMs in your own configuration file (e.g. ~/.asoundrc), or you can use the
pre-defined bluealsa PCM.

The Predefined bluealsa PCM
The simplest way to use the PCM plugin is with the predefined ALSA PCM device bluealsa.
The definition of this PCM device is of type plug so audio format conversion, if required,
is done automatically by the PCM. It has parameters DEV, PROFILE, CODEC, VOL, SOFTVOL,
DELAY, and SRV. All these parameters have defaults. Parameter values in an ALSA PCM name
are specified using the syntax:

bluealsa:DEV=01:23:45:67:89:AB,PROFILE=a2dp,CODEC=aac,VOL=60,SOFTVOL=no,DELAY=0,SRV=org.bluealsa

PCM Parameters
DEV The device Bluetooth address in the form XX:XX:XX:XX:XX:XX. Device names or
aliases are not valid here. The default value is 00:00:00:00:00:00 which selects
the most recently connected device of the chosen profile.

PROFILE
May be either a2dp or sco. sco selects either Hands-Free (HFP) or Headset (HSP)
profile, whichever is connected on the selected device. The default is a2dp.

CODEC Specifies the codec to be used by the profile. When a connection is established
between a device and a host, BlueALSA negotiates the best available codec with
the device; this parameter allows the ALSA configuration to override that
selection. The default value is unchanged which causes the PCM to use its
existing codec setting. The codec name is case insensitive; so for example aptX,
aptx, and APTX are all accepted. If the specified codec is not available the
plugin issues a warning and uses the default value instead.

For the A2DP profile it is possible to also specify a "configuration" for the
codec by appending the configuration as a hex string separated from the codec
name by a colon. For example:

CODEC=aptx:4f0000000100ff

VOL Specifies the initial volume for the PCM when opened. The default value is
unchanged which causes the PCM to use its existing volume setting. The value is
an integer percentage of the maximum volume [0-100]. The mute status can also be
set by appending the character '-' to mute the sound or '+' to unmute it. The
volume is not restored to its original value when the PCM is closed. For example
to set the initial volume to 80% and ensure that mute is disabled for this PCM:

VOL=80+

SOFTVOL
Enables or disables BlueALSA's software volume feature for this PCM. See the
bluealsa(8) manual page for more information on software volume. This is a
boolean option (values on or off), but also accepts the special value unchanged
which causes the PCM to use its existing softvol value. The default value is
unchanged.

DELAY An integer number which is added to the reported latency value in order to
manually adjust the audio synchronization. It is not normally required and
defaults to 0.

SRV The D-Bus service name of the BlueALSA daemon. Defaults to org.bluealsa. See
bluealsa(8) for more information. Not normally required.

Setting Different Defaults
The defaults can be overridden by defining the ones you want to change in your own
configuration (e.g. in ~/.asoundrc.conf) for example:

defaults.bluealsa.device "00:11:22:33:44:55"
defaults.bluealsa.profile "sco"
defaults.bluealsa.codec "cvsd"
defaults.bluealsa.volume "50+"
defaults.bluealsa.softvol off
defaults.bluealsa.delay 5000
defaults.bluealsa.service "org.bluealsa.source"

Positional Parameters
ALSA permits arguments to be given as positional parameters as an alternative to
explicitly naming them. When using positional parameters it is important that the values
are given in the correct sequence - DEV, PROFILE, CODEC, VOL, SOFTVOL, DELAY, SRV. For
example:

bluealsa:01:23:45:67:89:AB,a2dp,unchanged,unchanged,unchanged,0,org.bluealsa

When using positional parameters defaults can only be implied at the end of the id string,
so

bluealsa:01:23:45:67:89:AB

is equivalent to the full form above, but

bluealsa:01:23:45:67:89:AB,a2dp,,80+

is not permitted.

Defining BlueALSA PCMs
You can define your own ALSA PCM in the ALSA configuration. To do this, create an ALSA
configuration node defining a PCM with type bluealsa. The configuration node has the
following fields:

pcm.name {
type bluealsa # Bluetooth PCM
device STR # Device address in format XX:XX:XX:XX:XX:XX
profile STR # Profile type (a2dp or sco)
[codec STR] # Preferred codec
[volume STR] # Initial volume for this PCM
[softvol BOOLEAN] # Enable/disable BlueALSA's software volume
[delay INT] # Extra delay (frames) to be reported (default 0)
[service STR] # DBus name of service (default org.bluealsa)
}

The device and profile fields must be specified so that the plugin can select the correct
Bluetooth transport; the other fields are optional. Note that the default values for the
optional fields are not overridden automatically by the configuration defaults.bluealsa.*
in a PCM defined this way; however the configuration defaults can be referenced by use of
@func refer (see the ALSA configuration file syntax documentation for more information).

When choosing a name for your PCM definition, the name pcm.bluealsa is pre-defined by the
bluez-alsa installation (see section The Predefined bluealsa PCM above), so it should not
be used as a name for your own PCM devices as doing so will most likely have unexpected or
undesirable results.

Note that the volume field is of type string, so the value must be enclosed in
double-quotes. See the PCM Parameters section above for more information on each field.

Do not confuse the PCM type bluealsa with the PCM named bluealsa. The type does not
perform any audio conversions, you will have to wrap your own defined PCMs with type plug
to achieve that; whereas the predefined PCM pcm.bluealsa is of type plug.

Name Hints
Applications that follow ALSA guidelines will obtain the list of defined PCMs by using the
alsa-lib namehints API. To make BlueALSA PCMs visible via that API it is necessary to add
a "hint" section to the ALSA configuration. If you have defined a new PCM, then the hint
goes into the PCM configuration entry as follows:

pcm.bt-headphones {
type plug
slave.pcm {
type bluealsa
device "00:11:22:33:44:55"
profile "a2dp"
}
hint {
show on
description "My Bluetooth headphones"
}
}

Now using aplay -L will include the following in its output:

# aplay -L
bt-headphones
My Bluetooth headphones
#

If you are using the pre-defined bluealsa PCM, then you can create a "namehint" entry in
your ~/.asoundrc file like this:

namehint.pcm {
mybluealsadevice "bluealsa:DEV=00:11:22:33:44:55,PROFILE=a2dp|My Bluetooth headphones"
}

Then aplay -L shows

# aplay -L
bluealsa:DEV=00:11:22:33:44:55,PROFILE=a2dp
My Bluetooth headphones

For alsa-lib versions before v1.2.3.2, a bug in the namehint parser means that a
namehint.pcm entry has to be written as

namehint.pcm {
mybluealsadevice "bluealsa:DEV=00:11:22:33:44:55,PROFILE=a2dp|DESCMy Bluetooth headphones"
}

(note the keyword DESC after the pipe symbol and before the description text.)

With that hint in place, the PCM will be listed as both a Capture and Playback device. So
arecord -L will also list it. That is generally OK for HFP/HSP devices, but an A2DP device
most often offers only Capture (e.g. a mobile phone) or only Playback (e.g. a Bluetooth
speaker). It is possible to use the hint description to limit the listing to only one
direction using an undocumented syntax of ALSA configuration files.

If the hint.description value ends with |IOIDInput the PCM will only show in listings of
Capture devices; if it ends with |IOIDOutput the PCM will only show in listings of
Playback devices.

So we can modify our example above to:

pcm.bt-headphones {
type plug
slave.pcm {
type bluealsa
device "00:11:22:33:44:55"
profile "a2dp"
}
hint {
show on
description "My Bluetooth headphones|IOIDOutput"
}
}

namehint.pcm {
mybluealsadevice "bluealsa:DEV=00:11:22:33:44:55,PROFILE=a2dp|My Bluetooth headphones|IOIDOutput"
}

Now the aplay -L output will be exactly the same as before, but arecord -L will not
include bt-headphones in its output.

When using the namehint.pcm method, the key (mybluealsadevice in the above example) must
be unique but otherwise is not used. The first part of the value string, before the pipe |
symbol, is the string that is to be passed to ALSA applications to identify the PCM (e.g.
with aplay -D ...). The next section, after the pipe symbol, is the description that will
be presented to the user. The optional |IOID section is not included in the description
given to the application.

CTL PLUGIN

The BlueALSA ALSA CTL plugin can be used to define ALSA CTLs (mixer devices) in your own
configuration file (e.g. ~/.asoundrc), or you can use the pre-defined configuration that
is included in the bluez-alsa project.

A BlueALSA CTL device has no associated soundcard, so alsamixer will not list it in its F6
menu. It can be selected either by starting alsamixer with

alsamixer -D bluealsa

or by selecting "enter device name .." on the F6 menu then typing out "bluealsa" in the
"Device Name" box.

The CTL has two operating modes, Default mode and Single Device mode.

Default Mode
In this mode when a device connects, the mixer will create new controls for it, and when a
device disconnects, the mixer will remove its controls. alsamixer(1) will show these
changes dynamically.

Control names are constructed by combining the device Bluetooth alias with either the
profile type ('A2DP' or 'SCO') of the controlled PCM or the word "Battery" for battery
level indicators. If two or more connected devices have the same alias then an index
number is added to the name to make it unique.

The Bluetooth "alias" of a device is by default the same as its "name". The name is a
string defined by the device manufacturer and embedded in its firmware. Typically two
identical devices will have identical names. The "alias" is created by BlueZ and stored
locally on the host computer. So the alias can be changed using a tool such as
bluetoothctl(1) to make it unique if desired. As manufacturers tend to use long names for
their devices the alias can also be useful to give a short "nickname" to a device.

Although this default mode works well with alsamixer, there are some limitations that may
make it unsuitable for some applications. In particular:

• If device aliases are not unique then the index number associated with each is not
easily predictable in advance; so it can be difficult to programmatically associate a
PCM with its volume control.

• A consequence of the alsa-lib implementation of controls is that when one Bluetooth
device connects or disconnects it is necessary to remove all controls from all devices
in the mixer and create a new set. This invalidates pointers held by applications and
can cause application crashes. (Hardware sound cards do not have randomly appearing and
disappearing controls, so many, or even most, applications are not programmed correctly
to deal with it.)

Single Device Mode
The BlueALSA CTL also implements an alternative mode that presents controls only for one
specified device. In this case the control names are simply the profile type of the
controlled PCM ('A2DP' or 'SCO') or the word "Battery". There is never any need for index
suffixes or device alias. Immediately this overcomes the two main issues of the default
mode.

Single device mode is achieved by including the device Bluetooth address as an argument to
the ALSA device id, for example:

alsamixer -D bluealsa:00:11:22:33:44:55

A notable difference between single-device mode and the default mode is in the cases of
the device not being connected when the mixer is opened, and when the device disconnects
while the mixer is open.

For the default mode, the mixer will still open, even if no devices are connected, but
will display no controls. In single device mode the open request will fail with an error
message.

Similarly, in default mode when a device disconnects the mixer remains open but removes
the set of controls and creates a new control set without the disconnected device. That
new set will be empty if no devices remain. If the device then re-connects the mixer will
again create a new set of controls with the newly connected device included.

In single device mode when its device disconnects then the mixer will close. The alsamixer
application will continue running with no associated device or controls, but will not
automatically re-open the mixer if the device re-connects. The user can use F6 to open a
new device.

As a special case, a single device mixer can be opened with the address 00:00:00:00:00:00.
This will create a mixer with controls for the most recently connected device at the time
the mixer is opened. Once created, that mixer behaves the same as if it had been opened
with the actual address of the device: it does not change to a new device if another is
subsequently connected.

The Predefined bluealsa CTL
The bluealsa CTL has parameters DEV, BAT, and SRV. All the parameters have defaults.

CTL Parameters
DEV The device Bluetooth address in the form XX:XX:XX:XX:XX:XX. Device names or
aliases are not valid here. The default value is FF:FF:FF:FF:FF:FF which selects
controls from all connected devices (see Default Mode above). Also accepts the
special address 00:00:00:00:00:00 which selects the most recently connected
device.

BAT Causes the plugin to include a (read-only) battery level indicator, provided the
device supports this. If the value is yes then the battery indicator is enabled,
any other value disables it. The default is yes

SRV The D-Bus service name of the BlueALSA daemon. Defaults to org.bluealsa. See
bluealsa(8) for more information.

The default values can be overridden in the ALSA configuration, for example:

defaults.bluealsa.ctl.device "00:11:22:33:44:55"
defaults.bluealsa.ctl.battery "no"

Defining BlueALSA CTLs
You can define your own ALSA CTL in the ALSA configuration. To do this, create an ALSA
configuration node defining a CTL with type bluealsa. The configuration node has the
following fields:

ctl.name {
type bluealsa # Bluetooth PCM
[device STR] # Device address (default "FF:FF:FF:FF:FF:FF")
[battery STR] # Include battery level indicator (yes/no, default no)
[service STR] # D-Bus name of service (default "org.bluealsa")
}

All the fields (except type) are optional. See the CTL Parameters section above for more
information on each field. Note that the battery default value is no when used in this
way. As for PCM definitions above, the default values for the optional fields are
hard-coded into the plugin; they are not overridden by the configuration
defaults.bluealsa. settings.

FILES

       /etc/alsa/conf.d/20-bluealsa.conf
              BlueALSA  device  configuration  file.   ALSA additional configuration, defines the
              bluealsa PCM and CTL devices.

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