OBS writes uncompressed by default, and an hour is a lot of gigabytes
Screen recordings are the largest files most Macs ever create. Where OBS puts them, the settings that halve the size, and what to keep.
A screen recording is the largest thing most Macs produce. The default settings in most capture tools favour quality and speed of writing over size, which is correct while recording and expensive afterwards, because nothing ever revisits those settings.
Find what you have recorded
du -sh ~/Movies/* 2>/dev/null | sort -h | tail -10
find ~/Movies ~/Desktop ~/Downloads -name '*.mkv' -o -name '*.mov' -o -name '*.mp4' \
-size +500M 2>/dev/null | head -20The second command catches recordings that ended up outside the folder you expect, which is common when the output path was changed for one session and never changed back.
The settings that matter
| Setting | Default effect | Better for size |
|---|---|---|
| Recording format | MKV, safe against crashes | Keep, then remux to MP4 |
| Encoder | Often software x264 | Apple hardware encoder |
| Rate control | CBR at a high bitrate | CQP or CRF, quality based |
| Resolution | Full display, often 4K | Downscale to 1080p if that is the output |
| Replay buffer | Holds minutes in memory and on disk | Off unless you use it |
The hardware encoder on Apple silicon produces a much smaller file for the same visual quality and uses less power doing it, which makes it the single setting worth changing.
Remuxing rather than re-encoding
Recording to MKV protects you from a crash but the file is awkward to edit. Remuxing to MP4 rewrites the container without touching the video, so it is fast and lossless. It does not reduce the size; that comes from the encoder settings above.
The habit
- Export or publish the recording.
- Keep the export, not the raw capture, unless you will genuinely re-edit.
- Move anything worth keeping to an external drive or cloud storage.
- Check ~/Movies twice a year, since recordings are kept out of caution.
Video is near the top of the order to free 100 GB for exactly this reason, and the same trap appears with meeting recordings, which are saved to Documents at full size by default.
Common questions
Where does OBS save recordings on a Mac?
In the output path set in its settings, which defaults to ~/Movies. Changing it for one session and forgetting is common, so it is worth searching Desktop and Downloads for large video files too.
How do I make screen recordings smaller?
Use the Apple hardware encoder rather than software x264, switch to quality based rate control, and downscale to the resolution you actually publish at. Together these can more than halve the file size.
Should I record to MKV or MP4?
MKV is safer against a crash because it stays playable, then remux to MP4 afterwards. Remuxing rewrites the container without re-encoding, so it is fast and loses nothing.
Does the replay buffer use disk space?
It holds recent footage in memory and writes it out when triggered, so it costs space per save and keeps the encoder running continuously. Turn it off if you never use it.