Convert MP3 to captions

Create accessible closed captions from your MP3 audio. Sonix generates ADA-compliant captions with speaker identification and timing precision, helping you meet accessibility requirements for all media content.

ADA compliant
5-min turnaround
Accessible
Audio
Video
DOCX
SRT/VTT
PDF
53+ Languages
About This Format

Understanding MP3 files

What is a MP3 file?

Universal audio format supported everywhere

MP3 files are one of the most common audio file formats. Almost every player on any platform can open an mp3 file. The MP3 file format is a compressed file format with an intentional loss of audio quality. However, the loss should be negligible for the typical user. It was developed by the Moving Picture Experts Group (MPEG) and uses ‘Layer 3’ audio compression.
The audio compression preserves the audio within a normal human’s hearing range, while discarding unnecessary information outside of that range. MP3 files are usually used to store music and audiobooks with ‘near-CD quality sound’ (aka Stereo at 16-bit), but due to the great compression algorithm, the file size is around 1/10th of the WAV or AIF file equivalent. The quality of an MP3 file depends largely on the compression bit rate. Common bit rates are 128, 160, 192, and 256 kbps. And higher bit rates result in higher quality files that also require more disk space. MP3 files are easily handled and transcribed by Sonix, please try to upload higher bitrate quality audio files which will improve your transcript’s accuracy.

Common Uses

  • Music distribution
  • Podcast episodes
  • Audiobooks
  • Voice recordings
  • Music streaming

Audio Quality

Lossy compression; 192kbps+ indistinguishable from CD quality

Transcription Tips for MP3

  • 128kbps or higher recommended for accurate transcription
  • Very common format - Sonix handles all MP3 files
  • Variable bitrate (VBR) MP3s work fine
  • Avoid very low bitrates (below 96kbps) for speech

Where MP3 Files Come From

  • Spotify downloads
  • Podcast apps
  • Music players
  • Voice recorders
  • Web downloads
10x
Faster than real-time
Get your MP3 captions in minutes
99%
Accuracy rate
Industry-leading AI for MP3 files
53+
Languages
Captions in any language
30+
Export formats
SRT, VTT, SCC, and more
How It Works

Create captions from MP3 in 6 steps

Step 1

Create account

Sign up for Sonix's free trial. Includes 30 minutes free.

Step 2

Upload file

Upload your MP3 file from your computer or cloud storage.

Step 3

Select language

Choose from 53+ languages spoken in your file.

Step 4

Auto-transcribe

Sonix AI transcribes your MP3 with word-level timestamps.

Step 5

Edit captions

Fine-tune timing and formatting for accessibility.

Step 6

Export

Download closed captions in SRT, VTT, or SCC format.

Common Questions

Everything about MP3 captions

What's the difference between captions and subtitles for MP3?

Captions are designed for deaf and hard-of-hearing viewers, including speaker identification and sound descriptions. Subtitles assume the viewer can hear and focus on translating dialogue. For accessibility compliance, choose captions. Sonix supports both from your MP3 source.

Are MP3-to-caption conversions ADA compliant?

Sonix generates captions that meet ADA and Section 508 accessibility requirements when you include speaker labels and review for accuracy. The 99%+ accuracy from AI transcription provides an excellent foundation - a quick review ensures full compliance.

Can I add sound descriptions to MP3 captions?

Yes! After transcription, use Sonix's editor to add non-speech audio descriptions like [music playing], [door closes], or [applause]. This context helps deaf viewers fully understand the audio content beyond just the spoken words.

How do I indicate different speakers in MP3 captions?

Sonix automatically detects and labels different speakers during transcription. Before exporting captions, you can customize speaker names (e.g., change 'Speaker 1' to 'Host' or 'John'). Speaker labels appear at the start of each caption segment.

What caption format works for broadcast from MP3?

For broadcast television, export to SCC or STL formats which meet FCC closed captioning requirements. Sonix supports these professional broadcast formats alongside web-friendly options like SRT and VTT.

How accurate are AI-generated captions from MP3?

Sonix achieves 99%+ accuracy on clear MP3 audio, exceeding the 99% accuracy threshold recommended for professional captioning. For critical accessibility applications, we recommend a quick human review after AI transcription to catch any edge cases.

Why Sonix

Accessible captions from MP3 files

Accessibility First

Create captions that make your content accessible to deaf and hard-of-hearing viewers.

ADA Compliant

Meet accessibility requirements with properly formatted closed captions.

Sound Descriptions

Add non-speech elements like [music] and [applause] for full context.

SEO Benefits

Captions make video content searchable and improve discoverability.

Reviews

Trusted by accessibility teams

4.98 rating from 211 reviews

Your transcription tool is amazing. It's easy to use and gave me a great result.
MI
Marcio I.
Rio de Janiero, Brazil
Sonix is easy to use. Ridiculously easy. And even though the accuracy wasn't perfect it saved several days in a typical transcription cycle and the hourly cost we usually pay.
KA
Kyle A.
San Francisco, CA USA
I'd give Sonix a 10 mainly due to the accuracy.
CH
Cliff H.
Auckland, New Zealand
Incredibly fast return! Amazingly accurate transcription and exceptionally affordable!
GS
Guillermina S.
Schenectady, NY USA
Your product is incredible. I love it!
DC
David C.
Innsbruck, Austria
I love how accurate the software is! The way you can play audio as you go through the text or click on any part of the text to hear the audio is amazing.
BI
Bruce I.
San Diego, CA USA
Get Started

Create MP3 captions now

Try Sonix free with 30 minutes minutes of transcription. No credit card required.

99% accuracy. Every word matters.

AI transcription and translation in 53+ languages.

30 minutes free
No credit card
Cancel anytime