Settings for this task
| Use case | Setting | What to check |
|---|---|---|
| Interview | MP3 · 96 kbps · mono | Prioritize understandable consonants; check noisy sections. |
| Music | MP3 · 192 kbps · stereo | Keep spatial information and compare transients. |
| Small preview | MP3 · 64 kbps | Use when compactness matters more than fidelity. |
How to use this tool
- Upload an audio file and check its measured duration and codec.
- Choose a bitrate preset, or select a target-size preset if the upload budget matters most.
- Process the file, compare the reported sizes and listen before replacing any copy.
Calculated size examples
Calculated, not measured uploads: bytes ≈ bitrate (kb/s) × seconds × 1,000 ÷ 8. MB here means 1,000,000 bytes. Headers, tags and variable bitrate affect actual size. Channels are already included in the total bitrate; do not multiply again.
| Output duration | Format | Bitrate | Estimated audio payload |
|---|---|---|---|
| 5:00 | MP3 | 160 kb/s | 6 MB |
| 30:00 | MP3 | 96 kb/s | 21.6 MB |
What actually becomes smaller
FFmpeg decodes your recording and encodes a new MP3 on the server. Lowering the bitrate gives the encoder fewer bits for each second. This can remove detail, especially cymbals, reverberation and background texture. A WAV source often shrinks substantially; an already efficient AAC or Opus recording may not.
Speech, music and channel choices
Mono is useful for a single microphone, but removes stereo positioning. At the same total MP3 bitrate it does not halve the file size: the benefit is being able to try a lower bitrate for one channel. Preserve stereo for music unless the left-right information is unnecessary. Leave the sample rate unchanged unless a receiving application requires otherwise.
If the result is still too large
Check duration first, then lower the bitrate or trim an unnecessary introduction. Target presets calculate a bitrate from duration but codec rounding and headers affect the final size. Repeatedly compressing the last output compounds losses; return to your original file for each comparison.
Questions about this operation
- Is this a studio audio compressor?
- No. It reduces the number of bytes in a file. Use loudness normalization for listening-level adjustments; that is a different operation.
- Can I keep the original WAV?
- Yes: download a separate MP3 copy and keep your source locally. MP3 is lossy, so it should not replace a recording master.
- Why did my file grow?
- Your source may have a lower bitrate than the chosen MP3 setting. Compare the original and output sizes, then choose a lower setting or keep the source.
- Does 320 kbps repair a poor recording?
- No. Higher bitrate can limit additional encoding damage but cannot restore missing detail. Start with the best available source.
- Are the examples measured uploads?
- No: the size table is calculated from bitrate and duration. Headers, tags and encoder behavior make real output differ slightly.