BTA2DPD(8) System Manager's Manual BTA2DPD(8)

bta2dpd
Bluetooth Advanced Audio Distribution Profile daemon

bta2dpd [-Dv] [-A bitpool_allocation] [-B bitpool] [-b blocks] [-d device] [-e encoding_bands] [-f channel_mode] [-M mtu] [-m mode] [-r rate] [-V volume] -a address files ...

bta2dpd -K [-DIv] [-A bitpool_allocation] [-B bitpool] [-b blocks] [-d device] [-e encoding_bands] [-f channel_mode] [-m mode] [-p psm] [-r rate] [a address] file

bta2dpd -t [-A bitpool_allocation] [-B bitpool] [-b blocks] [-e encoding_bands] [-f channel_mode] [-M mtu] [-r rate] [-V volume] files ...

bta2dpd -t -K file

The bta2dpd daemon is used to transmit/receive audio to/from Bluetooth devices such as speakers or headphones, using the Advanced Audio Distribution Profile (A2DP).
address
Remote device address. The address may be given as BDADDR or a name.

If a name was specified, bta2dpd attempts to resolve the name via bt_gethostbyname(3).

bitpool
Allows setting the maximum bitpool value for your device. This may have to be lowered if audio is distorted.

Use bta2dpd with only the -v option and the maximum bitpool for your device will be printed to stdout.

Run in the background.
device
Local device address. May be given as BDADDR or device name.
Initiate a Discover command.
Useful when used as an audio sink as some devices need this to pair.
Allows registering as an audio sink receiving an incoming connection.
mtu
Allows setting the Maximum Transmission Unit (MTU) for the streaming connections.

For most devices this would be 672 but if audio is broken or has gaps lowering this value may help.

mode
Set L2CAP connection link mode. Supported modes are:

auth
Require devices to be paired.
encrypt
Auth, plus enable encryption.
secure
Encryption, plus change of link key.
psm
Allows changing the l2cap psm for an audio sink the default is 25. Most all devices will use 25.
Test mode can be used with -K to decode and receive encoded music from stdout/stdin to file.
volume
Allows shifting the volume of the music by 1 or 2 bits prior to encoding for increased volume.

USE WITH CARE as this may mean the output is quite loud.

Be verbose.
files ...
Files to stream. These can be WAV files or CD-Audio Red Book data or output from a pad(4) device. If not specified, the default is stdin or stdout if -K applied and bta2dpd is used as an audio sink.

When writing to a file or stdout it is raw 16-bit little endian (pulse coded modulation) PCM data. So a utility must be used to convert the file to add a header or use the audioplay(1) command as stated in EXAMPLES.

channel_mode
0
This specifies that all possible input formats are accepted and then one is chosen starting with joint stereo then stereo then 2 channel then mono.
m
This specifies that the input is monophonic.
2
This specifies that the input is dual-channel.
j
This specifies that the input is joint-stereo.
s
This specifies that the input is stereo. This is the default.

Specifying joint stereo as opposed to stereo would allow for a slightly higher quality of playback as bta2dpd will only encode stereo and monophonic streams.

rate
The frequency of the input. Where rate is one of 0, 16000, 32000, 44100, 48000. This defaults to 44.1 kHz.

A value of 0 will arbitrate from the highest to lowest frequency.

bitpool_allocation
0
Bit Allocation is negotiated starting with Loudness then SNR.
S
Audio is encoded with SNR (Signal to Noise Ratio) bit allocation.
L
Audio is encoded with Loudness bit allocation. This is the default.
blocks
Number of blocks to use for encoding. Where blocks is one of 0, 4, 8, 12, 16. This defaults to 16 blocks.

In the case of 0 the number of blocks is negotiated starting from 16 down to 4.

bands
0
Number of SBC bands is negotiated 8 then 4.
4
Audio is encoded with 4 SBC bands.
8
Audio is encoded with 8 SBC bands. This is the default.

It may be necessary to use btconfig(8) to set the class of your Bluetooth adapter to that of headphones when using bta2dpd as an audio sink. I.e.,

btconfig ubt0 class 0x200418
Then start bta2dpd with -K before pairing.

This is necessary as some devices only perform an sdpquery(1) just after pairing and cache the result.

It is possible to specify multiples of -r -e -b -f. This will mean that the specified combinations are reported as being accepted by the source/sink.

When used as a sink (-K), all modes, bands, blocks and allocation modes will be accepted unless specified as options. I.e., -r 44100 will only accept a connection with a rate of 44.1kHz.

bta2dpd -a spkr my.wav
Encode and send audio my.wav to address ‘spkr’.

bta2dpd -a spkr /dev/pad
Encode and send audio from pad(4) to address ‘spkr’.

bta2dpd -K out.pcm
Decode stream from any connected address and write it to out.pcm.

bta2dpd -K -a phone | audioplay -f -e linear -P 16 -s 44100 -c 2 --
Decode stream from address ‘phone’ and send to speakers.

audioplay(1), sdpquery(1), pad(4), btconfig(8)

Nathanial Sloss
July 27, 2019 NetBSD 9.4