SBC codec decrements bitpool value by fixed amount each time it is asked to
reduce output bitrate. This results in reduced audio quality with SBC codec.
Implement increase_encoder_bitrate for SBC codec by adding 1 to bitpool value
each time encoder bitrate needs to be increased to restore SBC audio quality.
While at it, remove bitpool decrement limit to use connection agreed value
instead as we will be able to restore quality later.
Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/474>
This API internally checks if a requested codec can be supported on the
system. This is especially required for codecs supported via GStreamer
where the availability of a plugin decides if the said codec can be
supported.
This will be used to prevent registration of a codec which the remote
endpoint device might be able to support, but, PulseAudio can't as the
codec is not available on the system due to the absence of a plugin.
We can also prevent listing or switching to an unavailable codec.
Note that the codec negotiation happens with the bluez stack even before
a device is connected. Because of this, we need to make sure that gst_init
is called before checking for the availability of a plugin. Since
module-bluez5-device gets loaded only after a connection to the device
has been established, doing the gst_init in that or one of the bluetooth
modules is not feasible.
Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/440>
Rename struct rtp_payload to rtp_sbc_payload as it is specific for SBC
codec payload.
Add proper checks for endianity in rtp.h header and use uint8_t type
where appropriated.
Field frame_count is only 4 bit number, so add checks to prevent overflow.
And because is_fragmented field is not parsed by decoder there is no
support for decoding fragmented SBC frames. So throw an error in this case.
Add explanation why minimal bitpool value is used in SBC codec as initial
bitpool value for A2DP source.
Set buffer size for reading/writing from/to A2DP socket to exact link MTU
value. This would ensure that A2DP codec does not produce larger packet as
maximal possible size which can be sent.
Because A2DP socket is of SOCK_SEQPACKET type, it is guaranteed that
we do not read two packets via one read/recvmsg call.
Properly check for all return values of encode/encode methods of A2DP codec
functions. They may fail at different levels. Also encode or decode API
method may return zero length buffer (e.g. because of algorithmic delay of
codec), so do not fail in this case.
The warnings:
modules/bluetooth/a2dp-codec-sbc.c: In function ‘default_bitpool’:
modules/bluetooth/a2dp-codec-sbc.c:161:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
switch (mode) {
^~~~~~
modules/bluetooth/a2dp-codec-sbc.c:169:9: note: here
case SBC_SAMPLING_FREQ_44100:
^~~~
modules/bluetooth/a2dp-codec-sbc.c:170:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
switch (mode) {
^~~~~~
modules/bluetooth/a2dp-codec-sbc.c:180:9: note: here
case SBC_SAMPLING_FREQ_48000:
^~~~
These were valid warnings in that an invalid channel mode would result
in unintended fallthroughs, but the end result would anyway been a crash
in the pa_assert_not_reached() at the end of the function, so
functionally there's no change.
Pulseaudio SBC codec defines that audio samples are in PA_SAMPLE_S16LE
format which is little endian. But libsbc library expects audio samples by
default in host endianity which is big endian on big endian system. So SBC
support on big endian system is broken. To fix this problem tell libsbc
library that audio samples are in little endian to match PA_SIMPLE_S16LE
sample format.
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=91359
Remove dead code and replace numeric bitpool values by macro definitions.
Maximal bitpool value in fill_capabilities() was reduced from 64 to 53
(SBC_BITPOOL_HQ_JOINT_STEREO_44100) because default_bitpool() already set
maximal value to 53.
This patch does not change SBC behavior as maximal bitpool was already
limited to 53. So it is just clean up.
This patch introduce new modular API for bluetooth A2DP codecs. Its
benefits are:
* bluez5-util and module-bluez5-device does not contain any codec specific
code, they are codec independent.
* For adding new A2DP codec it is needed just to adjust one table in
a2dp-codec-util.c file. All codec specific functions are in separate
codec file.
* Support for backchannel (microphone voice). Some A2DP codecs (like
FastStream or aptX Low Latency) are bi-directional and can be used for
both music playback and audio call.
* Support for more configurations per codec. This allows to implement low
quality mode of some codec together with high quality.
Current SBC codec implementation was moved from bluez5-util and
module-bluez5-device to its own file and converted to this new A2DP API.
