Convert AU to captions

Sonix transcribes your AU file and creates closed captions that make your content accessible to everyone.

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ADA compliant
5-min turnaround
Accessible
AU conversion guide

Create captions from AU 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 AU 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 AU 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 AU file format

Understanding AU files

What is a AU file?

Audacity project audio chunks

Audacity, an open source audio editor, breaks long tracks into small pieces so it can edit them more efficiently. Thus, when you save an Audacity Project File (.AUP), Audacity will automatically create a _data folder that has the same name as the AUP file and breaks the longer audio file into smaller chunks that have the .AU extension. Thus, when Audacity opens up the AUP Project File, it loads the individual AU files in the correct sequence automatically. The user should not move or rename and AU files in the _data folder.

Common uses for AU files

  • Audacity audio editing
  • Audio project files
  • Audacity project folders

Who works with AU files?

Podcast editors and home-studio producers usually run into AU files when recovering audio from legacy Audacity projects, since older versions of the editor stored each track as small AU chunks. Unix system administrators and Java developers may also recognize the format from its origins as the standard sound file on Sun and NeXT workstations.

AU vs WAV: which should you use?

AU and WAV are both simple header-plus-data audio formats: WAV, created by Microsoft and IBM, became the de facto standard for uncompressed audio, while AU originated on Sun and NeXT systems and survives mainly in legacy Unix software and older Audacity project folders. Both can hold uncompressed PCM, but WAV has far broader support in modern editors, players, and web tools. Choose WAV when exporting or sharing audio; AU is typically something a legacy project or system hands to you rather than a format you pick.

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

AU captions: frequently asked questions

Can you create closed captions from AU files?

Yes! Sonix transcribes your AU file with precise timestamps and creates closed captions in standard formats.

What's the difference between subtitles and closed captions?

Closed captions include non-speech elements like [music], [applause], and speaker identification. They're designed for deaf and hard-of-hearing viewers.

Are Sonix captions ADA compliant?

Yes! Sonix captions meet accessibility requirements when properly reviewed and edited. Our editor helps ensure timing and accuracy standards.

What caption formats are supported?

Export captions as SRT, VTT, or TTML. Each format has specific use cases.

Can I add sound descriptions?

Yes! Use our editor to add [music], [laughter], and other non-speech descriptions for full accessibility.

Do captions help with SEO?

Absolutely! Captions make your video content searchable and improve accessibility, both of which can boost SEO rankings.

Why is my Audacity project folder full of small AU files?

Older versions of Audacity split a project's audio into small AU block files inside a _data folder so long tracks could be edited efficiently, and the .aup project file reassembles them in order. Avoid moving or renaming these chunks; open the project and export the audio instead.

How do I play a standalone AU file?

Standalone AU files use the Sun audio format and open in players such as VLC and editors such as Audacity. Converting to WAV or MP3 gives the broadest compatibility with modern software and devices.

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