Drop audio files or choose a batch. Review format, size and duration.
Choose Recommended compression, Smallest file, High quality or Custom settings, then press Compress to MP3 (or your selected format).
Compare original and output size, signed savings, size ratio and processing time. Listen to both when supported, then download individual results or a ZIP.
Match the format to the destination
MP3 uses LAME with CBR 128, 192, 256 or 320 kbps, or VBR Standard, High and Best at 44.1/48 kHz. Recommended keeps the existing 192 kbps default; Smallest file uses 128 kbps mono, and High quality uses 256 kbps with original channels. For speech, mono can reduce unnecessary stereo data. Preserve stereo for music where the stereo image matters.
Custom Opus offers 32, 96 or 160 kbps and resamples to 48 kHz. It can suit compact voice or music when the recipient supports Ogg Opus. OGG output uses Vorbis quality 2, 5 or 8. FLAC levels 0, 5 and 8 preserve decoded PCM at original rate and channels; compression level changes size and speed, not fidelity. These content-dependent formats have no accurate pre-encoding size estimate.
Understand the quality and size tradeoff
Lower lossy bitrates can reduce file size at the cost of detail. Re-encoding an existing MP3, Vorbis or Opus file can add loss. Higher bitrate does not recover lost sound, and an already compact source may grow. Saved percentage = (original bytes − output bytes) / original bytes × 100; a negative result means the output is larger. Output / original is shown separately as the size ratio.
WAV, MP3, FLAC, Ogg Vorbis, Ogg Opus and standard PCM AIFF inputs are supported within the limits below. Files are processed one at a time. The compressor creates listening copies without modifying originals, and omits tags and artwork. Preview support depends on the browser; downloading a result does not prove the operating system finished saving it.
Use mono/stereo MP3 (CBR/VBR), PCM WAV (8/16/24-bit), native FLAC (8/16/24-bit), single-stream Ogg Vorbis or Ogg Opus, or standard PCM AIFF (16/24-bit, including .aif). AIFC, chained streams, surround audio and encrypted files are unsupported. M4A/AAC uses the separate M4A to MP3 tool.
Which compression mode should I choose?
Recommended uses MP3 CBR 192 kbps and original channels. Smallest file uses MP3 CBR 128 kbps and mono, which downmixes stereo. High quality uses MP3 CBR 256 kbps and original channels. Custom settings also offer MP3 320 kbps or VBR, Ogg Vorbis, Opus and FLAC. These presets are starting points, not guarantees of size or perceived quality.
Does compression always make audio smaller?
No. A source already using efficient lossy compression can become larger, particularly at a higher output bitrate. The result shows actual bytes and a signed saving percentage: (original − output) / original × 100. Negative savings mean a larger output. Output / original is the size ratio. There is no target-size guarantee.
Can I compare sound quality?
Original and output listening controls appear after processing. Playback depends on the browser’s support for each codec. If a preview is unavailable, download and listen in a compatible player. Lossy re-encoding can discard detail and never restores earlier losses; FLAC preserves decoded PCM when rate and channels stay unchanged.
Are files uploaded, and what are the limits?
Audio is processed locally in a worker. Engine assets load on demand. Up to eight files run sequentially, each limited to 32 MB, 10 minutes and 64 MB decoded PCM (16 MB on devices reporting 2 GB RAM or less). Retained results are capped at 64 MB. Clear results to release memory. No paid API is used; tags and artwork are omitted.
What if part of a batch fails?
Each file shows its own status and recovery guidance. Download successful files individually or use Download All for a ZIP of successful results. Cancel terminates processing; queued files are marked cancelled. Retry after checking the file or reducing its duration. If ZIP preparation fails, download individually.
