Audio from bluetooth device is delayed by around 3 seconds

System:

Bug: Audio from bluetooth device is delayed by around 3 seconds. See https://github.com/rbn42/panon/issues/26.

Reproducible script:

import soundcard as sc
import numpy as np
sample_rate=44100
channel_count=2
fps=60

blocksize = sample_rate // fps
mics = sc.all_microphones(exclude_monitors=False)

streams = []

for mic in mics:
    stream = mic.recorder(
        sample_rate,
        channel_count,
        blocksize,
    )
    stream.__enter__()
    streams.append(stream)

for i,mic in enumerate(mics):
    print('Stream %d id:%s'%(i,mic.id))
    print('Stream %d name:%s'%(i,mic.name))

while True:
    msg=''
    for i,stream in enumerate(streams):
        data = stream.record(blocksize)
        if np.sum(data)==0:
            msg+='Stream %d:paused '%i
        else:
            msg+='Stream %d:playing '%i
    print(msg,end='\r')

Requires NumPy. Thanks to @rbn42 for creating the script.

[matanui159]

Sorry for the delay, mix of busyness and sleep. The times stay about the same constantly but the headset is still delayed by 3s. Playing the audio through other channels does not delay the audio and (when using Panon) selecting only the headset also does not delay the audio.

[bastibe]

Can I use concurrent.futures.ThreadPoolExecutor instead of a very short blocksize?

Probably, yes. I think CFFI releases the GIL while calling C functions, so that should be ok. (Don’t use async though. Async certainly does not work.)

But I think the blocksize is not a problem here.

So far, I had assumed that the latency was incurred in the record step. But you are right, this doesn’t make sense. If one record were to take three seconds, it would delay all other records as well. So SoundCard is probably pulling the data off the sound card as fast as it is produced (with the occasional missed block as we discussed), but the Bluetooth device on pulse somehow has a built-in delay of three seconds before it is even passed to SoundCard.