Free Online Screen Recorder
Record Your Screen with Audio — Mic, System Sound, or Both
Audio is where most screen recorders get confusing — permission dialogs, "no system audio on macOS" footnotes, muted surprises after upload. This guide covers the three ways to record sound with your screen, what each browser and OS actually supports today, and how to fix the common failures before they happen.
Open CastLens and record nowThe three audio modes
Mic only: your narration over the screen — works everywhere, ideal for tutorials and feedback. System/tab audio: the sound the computer plays — great for demoing apps, sites, or games. Both: CastLens mixes microphone and system sound into one track through the Web Audio API, so one file carries your voice and the app's audio together.
What each platform actually supports
Windows: full system audio in every Chromium browser — pick "Entire screen" and enable audio. macOS: tab audio always; whole-system audio on Chrome 141+ with macOS 14.2+ (older combos need a tab or a virtual audio device). Safari: screen + microphone. Firefox: tab and window audio where the platform allows. When a browser can't provide system audio, this recorder tells you immediately instead of delivering a silent file.
Recording a clean voiceover
Use the 3-second countdown to settle before speaking, keep the mic 15–25 cm away, and do a 5-second test recording to check levels — your voice should peak clearly without clipping. Pause during mistakes instead of stopping: paused time costs nothing, and the built-in trimmer removes any rough start or ending afterwards.
Fixing silent recordings
Silent system audio on Mac → share a Chrome tab instead of the screen, or update to Chrome 141+. Silent mic → check the browser's site-permission for the microphone and the OS input device. Audio present but badly synced → avoid recording through Bluetooth headsets, whose codecs add latency; a wired mic keeps lips and voice aligned.
FAQ
Can I record microphone and system audio at the same time?
Yes — enable both switches before starting. Both sources are mixed into a single audio track in the exported file, with the microphone's echo cancellation on by default.
Why can't I get system audio on my Mac?
Either the browser or macOS is older than Chrome 141 / macOS 14.2, or the picker's audio option wasn't enabled. Sharing a Chrome tab always captures the tab's sound regardless of versions — the reliable fallback.
Which audio format does the recording use?
MP4 output carries AAC; WebM output carries Opus — both standard, accepted by every editor and platform. No exotic codecs, nothing to install.
Can I remove audio or keep video only?
Simply leave both audio switches off before recording — you get a clean video-only file. Recording video-only also slightly reduces file size and CPU load.
Does trimming affect the audio sync?
No. The built-in trimmer re-encodes video and audio on the same timeline, cutting both tracks at your chosen in/out points, so sync is preserved to the frame.