OBS Studio
(obsproject.com) is
a powerful, free, and open-source software suite for video recording
and live streaming. It can combine multiple input video and audio
signals and record (or stream) them, and so is very useful for screen
and session capture. OBS Studio is available for Windows, Mac, and
Linux.
For the broadest compatibility with web browsers, the final recording should be in MP4 format, with an H.264 video codec and an AAC audio codec (OBS Studio records audio in AAC format by default). The best strategy is to record initally in MKV format, then later remux without loss of quality (File → Remux Recordings) to MP4 format.
If OBS somehow crashes during recording, an MP4 file cannot be closed properly and the recording is corrupted and lost. An MKV can be recovered.
These are some of the most important settings (for me on my machine):
o File → Settings → Output
  Output Mode:  Advanced - Recording
  Recording Settings
    Recording Format:  Matroska Video (.mkv)
    Video Encoder:     NVIDIA NVENC H.264  [hw encoder if available, else x264]
    Audio Encode:      CoreAudio AAC       [CoreAudio if available, else FFmpeg AAC]
  Encoder Settings
    Rate Control:      Variable Bitrate
    Bitrate:           5000 Kbps
    Maximum Bitrate:   6000 Kbps
  Output Mode:  Advanced - Audio
    set Audio Bitrate on each track to 192
o File → Settings → Audio
    Sample Rate:  44.1 kHz
    Channels:     Stereo
o File → Settings → Video
    Base (Canvas) Resolution:    3840×2160
    Output (Scaled) Resolution:  1920×1080
    Downscale Filter:            Lanczos (Sharpened scaling, 36 samples)
    Common FPS Values:  20
o File → Settings → Hotkeys
  Set Ctrl-Shift-F1 in *both* Start Recording and Stop Recording fields
  (so acts as toggle)
o File → Settings → Advanced
  Recording
    File Name Formatting
      %CCYY-%MM-%DD-%hh%mm%ss
o Add Sources - Window Capture (say Firefox) - Mic/Aux (select microphone) o Right-click on Window Capture - Resize output (source size)
If you are trying to capture a Chrome browser window, and all you see is an empty frame, try disabling hardware acceleration in Chrome Settings (Settings - System - Use hardware acceleration when available = Off).
Kezz Bracey;
How to Record Your Screen for Free With Open Broadcaster Software (OBS);
31 Jul 2024;
https://photography.tutsplus.com/tutorials/obs-for-screen-recording-quick-start--cms-28549
Vivian Tejeda;
Record with OBS;
14 Jul 2025;
https://descript.com/blog/article/how-to-record-with-obs
icedterminal;
CoreAudio;
02 Oct 2023;
https://github.com/icedterminal/CoreAudio
On Windows, install Apple's CoreAudio AAC encoder for better sound quality.