Tech
Convert MP4 to MP3 Online Free: Which Bitrate to Choose
Converting MP4 to MP3 takes seconds, but the bitrate you choose decides how it sounds and how big the file is. Here's what 128, 192 and 320 kbps really mean.
· 5 min read · RunConvert Team
Pulling the audio out of a video is one of the most common conversions there is. People turn lectures into something to listen to on a commute, save a song from a video they recorded at a gig, grab a voice memo that ended up as a screen recording, or make a podcast out of a webinar. You can convert MP4 to MP3 online in seconds, for free.
The part most people skip is the setting that decides how the result sounds: the bitrate. This article explains what the numbers mean, which one to choose, and the mistakes that leave you with a bloated file or a muddy recording. For the click-by-click walkthrough, see our MP4 to MP3 guide.
The Quick Version
- Open MP4 to MP3 and add your video (up to 1 GB).
- Optionally open the settings to pick a bitrate or trim the clip.
- Download your MP3. The video is discarded and only the audio is kept.
No account, no watermark, and the upload is deleted automatically after conversion.
What Bitrate Means
Bitrate is how much data is used to store each second of sound, measured in kilobits per second (kbps). More data means more detail and a bigger file. MP3 is a lossy format, so it throws away sounds you're unlikely to hear; the bitrate decides how much it throws away.
| Bitrate | Sounds like | Size per minute (approx.) | Use it for |
|---|---|---|---|
| 96 kbps | Clear speech, thin music | 0.7 MB | Long lectures, audiobooks on limited storage |
| 128 kbps | Good speech, decent music | 1 MB | Podcasts, voice notes, meetings |
| 192 kbps | Very good music | 1.4 MB | A sensible default for songs |
| 256 kbps | Excellent | 1.9 MB | Music you care about |
| 320 kbps | MP3's best | 2.4 MB | Archiving music, DJ sets |
The sizes are simple arithmetic: kilobits per second × 60 ÷ 8 gives kilobytes per minute. A 60-minute lecture at 128 kbps is about 58 MB; at 320 kbps it's about 144 MB, for no audible benefit on speech.
Which Bitrate Should You Pick?
- Speech (lectures, interviews, meetings, podcasts): 128 kbps. Voices don't need more, and you'll fit far more hours on a phone.
- Music: 192 kbps is the sweet spot. Most people can't tell it apart from 320 kbps on phone speakers or ordinary earbuds.
- Music you'll edit, remix or archive: 320 kbps, or skip MP3 and use a lossless format (see below).
Mistake 1: Choosing a Higher Bitrate Than the Source
This catches a lot of people. Most MP4 videos already store their audio in a compressed format called AAC, often at 128 or 160 kbps for phone recordings and social media downloads. Converting that to a 320 kbps MP3 doesn't bring back detail that was never there. You just get a file twice the size of the same sound.
A good rule: match the source or go one step above it. If you don't know the source bitrate, 192 kbps is a safe middle ground.
Mistake 2: Converting the Same Audio Again and Again
Every lossy conversion throws away a little more. AAC to MP3 is one lossy step, which is fine. MP3 to AAC to MP3 is three, and the losses add up into a swirly, metallic sound. Always convert from the original video, not from a previous MP3.
Mistake 3: Using MP3 When You Need Lossless
If the audio is going into editing software, a DAW or a transcription tool that's sensitive to quality, use a lossless format instead:
- MP4 to WAV: uncompressed, universally supported, large files.
- MP4 to FLAC: lossless compression, about half the size of WAV.
- MP4 to M4A: can keep the original AAC audio without re-encoding, ideal for Apple devices.
Not sure which audio format fits? Our comparison of MP3 vs WAV vs FLAC explains the trade-offs.
Mistake 4: Converting a Whole Video When You Need One Minute
If you only need the chorus, the key quote or one section of a webinar, use the trim option to set a start and end time before you convert. The MP3 comes out smaller, and you won't need to open an audio editor afterwards.
Other Videos, Same Process
The same steps work for any video format, not just MP4:
- MOV to MP3 for iPhone and Mac recordings.
- MKV to MP3 and WebM to MP3 for downloaded and browser-recorded video.
- M4A to MP3 when you already have the audio, but in a format your device doesn't like.
You can also convert several files in one batch. Add them all, pick MP3, and download the results together.
Is It Legal to Convert MP4 to MP3?
Converting your own recordings, lectures you're allowed to keep, or files you have the rights to is fine. Downloading and converting copyrighted music or videos you don't have permission to use is a different matter, and depends on the platform's terms and your local law. RunConvert converts files you upload. It doesn't download from streaming sites.
Convert Your MP4 to MP3 Now
Pick 128 kbps for speech or 192 kbps for music, trim what you don't need, and convert from the original video. Convert MP4 to MP3 free, or browse the audio converter for every other audio format.
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