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How can I know is LDAC loaded ?

Just check your log (systemlog or journald) and search "LDAC" or "SBC"

You can enable debug log by edit /etc/pulse/daemon.conf and set "log-level = 4"

Don't forget to run pulseaudio -k . Make sure your headphone/speaker have support of LDAC .

if LDAC loaded, you can see

N: [bluetooth][module-bluez5-device.c:795 ldac_process_render()] Using LDAC encoder version: 2.00.02

and log of bitrate printed once per minute (before git tag legacy)

D: [bluetooth][module-bluez5-device.c:2026 thread_func()] LDAC Transmission:: Average Speed: 990.00Kbps, Speed(60 sec): 990.00Kbps/s; QualityModeId: 0

if SBC loaded, you can see

D: [bluetooth][module-bluez5-device.c:551 a2dp_process_render()] Using SBC encoder implementation: MMX

Can I choose codec ?

No, A2DP codec is chosen by bluez. Though the order of codecs is declared in this module, it is arranged by quality of codec(LDAC > APTX HD > APTX > SBC). It means if your device support APTX,LDAC,SBC, bluez will choose LDAC codec as primary codec.

Bitrate of LDAC

abrQualityModeID	LDAC encode quality ⬇ | Input PCM frequency ➡	48khz, 96khz	44.1khz, 88.2khz
0	High Quality	990kbps	909kbps
1	Standard Quality	660kbps	606kbps
2	(ABR only)	492kbps	452kbps
3	(ABR only)	396kbps	363kbps
4	Mobile use Quality	330kbps	303kbps

LDAC Adaptive Bit Rate (ABR) mode detect the transmission quality and choosing LDAC encode quality as higher as possible.

Are there any plans to upstream this into Pulseaudio?

Sure，but I will wait Pali Rohár who at work on adding APTX support for Pulseaudio. You can check it at pulseaudio-discuss maillist . I will not join discussion about LDAC before they have a final solution about how multiply codec in pulseaudio mixed up. And my poor English is also a barrier.