Asynchronous Audio Filter Plugin for OBS Studio

Introduction

This plugin tries to fix an asynchronous audio by synchronizing to the master clock of OBS Studio.

OBS Studio is running with a clock provided by the OS. On Linux, the clock is synchronized to the NTP server. On the other hand, some audio interfaces are running with their own clock to sample the audio, which is asynchronous from the OBS's clock. The difference of these clocks causes the audio buffer to reach overflow or underflow after several minutes or more and causes OBS to drop a bunch of audio frames or to introduce silent frames.

This filter will detect the difference and periodically add or remove an audio sample. Since just one sample is added or removed at each time, distortion should not be noticable.

This filter won't resolve asynchronous issue when monitoring the audio. In some cases, the monitoring device has yet another sampling clock other than OBS Studio or source audio.

Properties

Use OBS time

This plugin assumes the timestamp set by the audio source is calculated from the function os_gettime_ns. If not, it is suggested to enable this option.

Verbosity

Increase or decrease verbosity in the log file.

Recommended settings

Recommended setting for each source type is listed below.

Type	Source settings	This filter settings
Audio Output Capture, Audio Input Capture	Uncheck Use Device Timestamps	Leave it as it is.
Application Audio Capture	n/a	Enable Use OBS time instead of source time.
V4L2	Uncheck Use Buffering	Leave it as it is.
Decklink	Uncheck Use Buffering	Leave it as it is.
Video Capture Device on macOS	Uncheck Use Buffering	Leave it as it is.
Video Capture Device on Windows	Uncheck Buffering	Leave it as it is.
NDI Source	Set Latency Mode to Low (experimental)	Enable Use OBS time instead of source time.

Note

Do not apply this plugin to a local file player such as Media Source and VLC Video Source.

Build and install

Linux

Install libsamplerate. Use apt as below on Ubuntu-22.04.

sudo apt install libsamplerate0 libsamplerate0-dev

Use cmake to build on Linux. After checkout, run these commands. The flags -D USE_ERIKD_LIBSAMPLERATE_DEPS=OFF -D USE_ERIKD_LIBSAMPLERATE_SYSTEM=ON are optional but recommended to ensure libsamplerate from the system will be linked.

mkdir build && cd build
cmake \
  -D CMAKE_INSTALL_PREFIX=/usr \
  -D USE_ERIKD_LIBSAMPLERATE_DEPS=OFF \
  -D USE_ERIKD_LIBSAMPLERATE_SYSTEM=ON \
  ..
make
sudo make install

If you prefer libswresample instead of libsamplerate, configure with these flags.

mkdir build && cd build
cmake \
  -D CMAKE_INSTALL_PREFIX=/usr \
  -D USE_ERIKD_LIBSAMPLERATE_DEPS=OFF \
  -D USE_ERIKD_LIBSAMPLERATE_SYSTEM=OFF \
  -D USE_FFMPEG_SWRESAMPLE=ON \
  ..
make
sudo make install

macOS

Use cmake to build on macOS. After checkout with a submodule, run these commands.

mkdir build && cd build
cmake ..
make