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.

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ADA compliant
5-min turnaround
Accessible
MP3 conversion guide

Create captions from MP3 in 6 steps

  1. 1
    Create account~30 sec

    Sign up for a free Sonix trial with 30 free minutes.

  2. 2
    Upload file~1 min

    Upload your MP3 file from your computer or cloud storage.

    44+ formats supported
  3. 3
    Select language~10 sec

    Select the language spoken in your file.

    54+ languages
  4. 4
    Auto-transcribe~5 min

    Sonix AI transcribes your MP3 with word-level timestamps.

  5. 5
    Edit captions~2 min

    Fine-tune timing and formatting for accessibility.

  6. 6
    Export~10 sec

    Download your closed captions as SRT or VTT files.

    30+ export formats
The MP3 file 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 for MP3 files

  • Music distribution
  • Podcast episodes
  • Audiobooks
  • Voice recordings
  • Music streaming
  • Spotify downloads
  • Podcast apps
  • Music players
  • Voice recorders
  • Web downloads

Who works with MP3 files?

Journalists, academic researchers, and oral historians frequently work with MP3 interviews because nearly every handheld recorder and dictation app can export the format. It is also a common delivery format for radio archives, lecture capture systems, and call-recording services that need small files that play on any device.

MP3 vs WAV: which should you use?

WAV files store uncompressed PCM audio, preserving the full recorded signal, but they are roughly ten times larger than an equivalent MP3. MP3 permanently discards audio detail that most listeners cannot hear, which keeps files small for sharing and playback but makes it a poor choice as an editing or archival master. Choose WAV when recording or producing source audio; choose MP3 when file size and universal compatibility matter more than maximum fidelity.

Convert WAV to text
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Get your MP3 captions in minutes
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Accuracy rate
Industry-leading AI for MP3 files
53+
Languages
Captions in any language
30+
Export formats
SRT, VTT, and TTML
MP3 conversion FAQ

MP3 captions: frequently asked questions

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 TTML 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.

Does the MP3 bitrate affect transcription quality?

It can. Files encoded at 128 kbps or higher preserve more speech detail, while heavily compressed recordings below about 96 kbps may introduce artifacts that make words harder to recognize.

How do I turn an MP3 recording into SRT subtitles?

Upload the MP3, generate a transcript, adjust the text and timings as needed, and export the result in SRT or VTT caption format.

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