MP3 Compressor

MP3 compression is the process of re-encoding an audio file at a lower bitrate — the number of kilobits per second (kbps) used to represent the audio data. A higher bitrate preserves more audio detail but produces a larger file; a lower bitrate produces a smaller file with some quality loss. MP3 uses perceptual audio coding (MPEG-1 Audio Layer III) to discard audio information that the human ear is least likely to notice — such as sounds masked by louder frequencies. Our free mp3 compressor online uses the Web Audio API to decode your audio to raw PCM and LameJS to re-encode it at your chosen bitrate — entirely in your browser with no server upload required.

1. Upload Your Audio File: Drop your MP3, WAV, M4A, or OGG file onto the drop zone or click to browse. Our mp3 compressor onlinedecodes the audio to raw PCM using the browser's Web Audio API — your file never leaves your device.
2. Choose Your Target Bitrate: Select from 6 bitrate presets — 320 kbps (highest quality) down to 64 kbps (voice-optimized). Each preset shows the quality level and estimated output size so you can choose the right balance for your use case.
3. Compress and Download:Click "Compress to [bitrate] kbps" — LameJS re-encodes the audio at your chosen bitrate and the compressed MP3 downloads automatically. The stats panel shows exact original vs compressed sizes and the percentage reduction.

• 320 kbps: Highest quality — virtually indistinguishable from lossless for most listeners. Use for music archiving and professional audio work.
• 192–256 kbps: High quality — excellent for music streaming and distribution. Most listeners cannot distinguish from 320 kbps.
• 128 kbps: Standard quality — the most common bitrate for music streaming. Good balance of quality and file size for general use.
• 64–96 kbps: Reduced quality — suitable for voice recordings, podcasts, and speech content where music fidelity is not required. Produces the smallest file sizes.

Re-encoding always introduces some quality loss — even at 320 kbps, re-encoding an already-compressed MP3 applies a second round of lossy compression. For best results, compress from a lossless source (WAV, FLAC) rather than re-compressing an existing MP3. The estimated output size shown before compression is calculated from the target bitrate and duration — the actual file size may vary slightly due to LameJS encoding overhead and VBR behavior.