Bluetooth audio play with OPUS codec on Raspberry Pi 3B+ has Crackles

[SaneBow]

Is this the right place for my bug report?
This seems like a kernel or firmware issue. I am not sure.

Describe the bug
I tried connecting to my bluetooth speaker and playing music on my Raspberry 3B+ with the onboard bluetooth. While listen to some music, I can hear many crackle sounds, especially when there are drum beats.
This only happen with Raspberry Pi bluetooth + OPUS codec audio file.

To reproduce
List the steps required to reproduce the issue.
Attached test.webm is a audio snippet where crackles are found. I play it with ffplay.
crackle_audio_test.zip

The test.m4a is converted with ffmpeg from the test.webm, in which the crackles disappear.
This may be related to OPUS codec family as I also tried to convert it to .ogg (Vorbis codec), it also has crackles.

System

• Which model of Raspberry Pi? Pi3B+
• Which OS and version (cat /etc/rpi-issue)?
  Raspberry Pi reference 2021-03-04
  Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 461109415073d2eb67083709662ba983cc191f14, stage
• Which firmware version (vcgencmd version)?
  version 564e5f9b852b23a330b1764bcf0b2d022a20afd0 (clean) (release) (start)
• Which kernel version (uname -a)?
  Linux raspberrypi 5.10.17-v7+ vchiq_arm: do not use page_cache_release(page) macro #1403 SMP Mon Feb 22 11:29:51 GMT 2021 armv7l GNU/Linux

Additional context
I tried with different combinations to locate the source of the problem:

• Raspberry Pi playing webm audio on my bluetooth speaker A --> has crackles
• Raspberry Pi playing webm audio on my speaker A with 3.5 mm jack --> no crackles
• Raspberry Pi playing webm audio on my bluetooth speaker B --> has crackles
• Raspberry Pi playing m4a audio on my bluetooth speaker A --> no crackles
• Macbook playing webm audio on my bluetooth speaker A --> no crackles

I also disabled onboard WiFi during the testing. So it's not because of the "WiFi interference with Bluetooth issue".

[SaneBow]

More testing indicates that it may not be related to bluetooth. Close this issue for now. Will reopen if I can narrow down this issue and confirm it's related to rPi kernel.

Edit: it seems to be cause by a known speexdsp resampler bug: xiongyihui/notes#16