NEW · FFmpeg.wasm · 100% Browser-Based

Audio Compressor

Shrink audio files with bitrate and quality presets — MP3, AAC, Opus. FFmpeg.wasm runs locally. No upload, no signup, no watermark.

🎵
Drop an audio file
MP3 · WAV · AAC · OGG · FLAC · M4A
Files stay on your device · Never uploaded

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Audio Extractor →
Strip the audio track from any video — MP3, WAV, AAC, or OGG.
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Browse the full Audio Suite — 7+ tools, all in-browser.

Why Do This in Your Browser?

Most audio compression questions are size-driven: a podcast episode that's 200MB needs to fit a hosting plan's bitrate budget; an audiobook chapter sits at twice the size it should be because the original was recorded uncompressed; a voice memo needs to ship under a 25MB email cap. The compression math is decades old, and every desktop audio tool wraps the same encoders this browser tool does — LAME for MP3, FAAC for AAC, Opus for Opus.

FFmpeg.wasm bundles all three encoders. The tool runs the same bitrate/VBR/quality math as desktop FFmpeg, locally, without uploads. Pick a target — typical voice content lands at 64–96kbps mono in Opus or 96–128kbps stereo MP3 — and the compression runs in seconds for typical files.

How It Works

Three output formats with sensible defaults. MP3 (LAME via FFmpeg): bitrate-based, VBR with quality 0–9 or fixed bitrate 32–320kbps. AAC: similar bitrate range, slightly more efficient than MP3 at low bitrates, defaults to MP4 container. Opus: most efficient at low bitrates (32–96kbps for voice), defaults to OGG container. Each format exposes either 'pick a bitrate' or 'pick a quality preset' modes.

Presets handle the common cases: Podcast Voice (64kbps mono Opus), Podcast Music (128kbps stereo MP3), Audiobook (96kbps mono MP3), Music Stream (192kbps stereo MP3), Hi-Quality (320kbps stereo MP3), Voice Memo (32kbps mono Opus). Custom mode exposes the underlying knobs.

Tip: If you need to extract audio from a video first, the Audio Extractor tool pulls the audio track without re-encoding when possible. For format conversion without a bitrate change, use the Audio Converter instead.

Common Use Cases

Podcast Hosting Caps
Most podcast hosts cap upload size or bandwidth per episode. Compress before upload to stay under the cap.
Audiobook Compression
Convert uncompressed WAV chapter files to 96kbps MP3 for distribution; 90%+ size reduction at imperceptible voice quality loss.
Voice Memo Sharing
iPhone voice memos export as 96kbps M4A by default. For Email/Slack sharing, 32kbps Opus is half the size with the same intelligibility.
Music Distribution
Standard 192kbps MP3 is the sweet spot for music streaming — small enough to stream on slow connections, near-transparent on most listening setups.
Archive Compression
Old uncompressed WAV recordings take 10–50x the space they need. Bulk-convert to Opus for ten-times-smaller archives without audible loss.
Mobile Upload Speed
Smaller files upload faster on mobile data. A 5-minute voice recording at 32kbps Opus is under 1.5MB.

How We Compare

Honest read on free, paid, and self-hosted options for this kind of job:

UDT Audio Compressor (this tool): Free, browser-based, FFmpeg.wasm runs LAME / FAAC / Opus locally. Six presets, full custom mode. No upload, no watermark, no signup.
CloudConvert: Cloud-based; free tier limited daily minutes; $9–$25/mo paid. Excellent format support; uploads required.
OnlineAudioConverter: Cloud-based; free tier with ads. Uploads required; file size caps.
Audacity (desktop): Free, open-source desktop editor. Full audio editing suite; this browser tool is the focused alternative for batch compression jobs.
iTunes / Music app: Free, can re-encode but limited to MP3/AAC and Apple's preferred bitrate ladder.
LAME / FFmpeg CLI: Free, command-line. Powerful and scriptable; this browser tool is FFmpeg + a UI.

Frequently Asked Questions

Is this audio compressor really free?+
Yes — completely free, no watermark, no time limits, no signup. The site is supported by ads elsewhere; the tool is unrestricted.
Which format should I pick — MP3, AAC, or Opus?+
Opus is the most efficient at low bitrates (best for voice and podcast); pick it when source compatibility allows. MP3 is universally supported, including by old hardware; pick it when you don't know the playback environment. AAC is slightly better than MP3 at the same bitrate and is the default on Apple platforms.
Are my audio files uploaded anywhere?+
No. FFmpeg.wasm runs entirely in your browser. The 32MB engine downloads once and caches; after that, the tool works fully offline.
Will I lose quality?+
Lossy compression always loses some quality — that's how it achieves the smaller file size. The question is whether the loss is audible. At 192kbps MP3, most listeners can't tell the difference from the source on consumer hardware. At 64kbps Opus, voice content is still very listenable; music has audible artifacts. Pick higher bitrates for archival quality, lower for streaming or sharing.
What's the difference between VBR and CBR?+
Variable bitrate (VBR) allocates more bits to complex passages and fewer to simple ones — overall file size is smaller for the same perceived quality. Constant bitrate (CBR) uses the same bitrate throughout — useful for streaming where playback systems prefer predictable bandwidth. The tool defaults to VBR for MP3 and AAC; Opus is inherently VBR.
Can I batch-compress multiple files?+
Yes — drop multiple files into the drop zone and the tool processes them sequentially, then offers a zip of the results.
What's the maximum file size?+
Limited by browser memory. Most laptops handle 500MB to 1GB audio files comfortably; phones cap around 200MB. For long-form content like multi-hour audiobooks, a desktop tool will be faster.
What's the underlying engine and license?+
FFmpeg.wasm v0.12.x with @ffmpeg/core v0.12.6 (LAME for MP3, FAAC for AAC, native Opus encoder built in). FFmpeg itself is LGPL-licensed; the wasm wrapper is MIT.

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