When a converter offers a quality menu, the instinct is to choose the highest number. For MP4 to MP3 conversion that instinct is usually wrong, and understanding why saves a surprising amount of disk space.

The reason comes down to a single principle: bitrate is a ceiling, not a floor. It caps how much data the encoder may use. It cannot manufacture detail that was not in the source.

What is actually inside your MP4

MP4 files carry AAC audio in the overwhelming majority of cases. The bitrate depends on where the file came from:

  • Phone recordings: typically 96 to 128 kbps AAC, often mono for voice.
  • Screen recordings and video calls: 64 to 128 kbps, optimised for speech.
  • Online video: commonly 128 kbps, sometimes 192 kbps for higher-quality streams.
  • Professionally produced video: 192 to 256 kbps AAC.
  • Camera footage: varies widely, sometimes uncompressed PCM on higher-end bodies.

So most of the time you are starting from something around 128 kbps. Encoding that at 320 kbps produces a file two and a half times larger that sounds identical to a 192 kbps version. The extra data is spent faithfully reproducing compression artefacts.

The settings and what they are for

320 kbps — about 2.4 MB per minute. Only justified when you know the video carries a high-bitrate music mix, or the audio is uncompressed PCM from a camera.

256 kbps — about 1.9 MB per minute. Ample headroom for anything a video is likely to contain.

192 kbps — about 1.4 MB per minute. The default, and the right answer for nearly every video. Comfortably above what most MP4 soundtracks contain, so nothing is lost in the transfer.

128 kbps — about 0.96 MB per minute. A good match when you know the source is a phone recording or a standard stream, since it matches rather than inflates.

96 kbps — about 0.72 MB per minute. The speech setting. A two-hour lecture becomes roughly 86 MB instead of 172 MB at 192 kbps, with no meaningful difference on a single voice.

Speech and music want different things

This is the distinction that matters most in practice, because it is the one that changes the answer by a factor of two.

Speech is acoustically simple: a narrow frequency range, one source at a time, and gaps between words. Lossy encoders handle it extremely efficiently, which is why podcasts routinely ship at 64 to 96 kbps and sound perfectly clear. If your MP4 is a lecture, an interview, a sermon, a meeting recording or an audiobook, 96 kbps is genuinely enough, and over a hundred hours of material the saving is real.

Music is the opposite: wide frequency range, many simultaneous sources, sustained complexity. Cymbals, strings, applause and dense electronic production are exactly what stresses an encoder. For anything musical, 192 kbps is the sensible floor.

How much can you actually hear?

Less than the marketing around high-bitrate audio suggests. Blind listening tests consistently show that above 192 kbps most listeners cannot reliably identify the higher-bitrate file — and that is with the original recording, not a soundtrack already compressed once inside a video.

For extracted video audio the point is even sharper. You are re-encoding something already lossy, so the ceiling was set by whoever produced the video. No setting here can raise it.

When to skip lossy entirely

If the audio is going into an editor rather than a music player — noise reduction, levelling, cutting several recordings together, or transcription — then any lossy setting is the wrong choice. Convert to WAV instead. There is no second lossy pass, editing operations compound cleanly, and you export to MP3 once at the end. The editing guide covers this workflow.

There is also M4A, which is worth considering precisely because it keeps the audio in the AAC family it started in. At 192 kbps AAC you get a slightly smaller file than the MP3 equivalent with slightly better fidelity — the catch being older hardware that only reads MP3.

The short answer

Use 192 kbps unless you have a reason not to. Drop to 96 kbps for speech. Go to 320 kbps only for genuinely high-quality music sources. And when in doubt, remember that a larger file is not automatically a better one.

Ready to convert? The MP4 to MP3 tool has all of these settings in its quality menu. If you have a folder to work through, the batch guide covers applying one setting across many files, and the step-by-step guide covers the process itself.