Audio formats

This page lists the audio formats each audio API accepts and returns. The feature pages link here instead of repeating the lists.

Transcription input

Each transcription mode takes audio in a different form:

Mode	How you send audio	Formats	Details
File transcription	One file per request: `file` (upload), `file_url` (a URL of up to 2,083 characters), or `file_id` (a file uploaded to `/v1/files` with `purpose=audio`)		File transcription
Realtime transcription	Raw audio in base64 chunks, described by `audio_format` in `session.update`	`pcm_s16le` (16-bit signed little-endian PCM, mono). Default sample rate: 16,000 Hz.	Realtime transcription

Speech output

Speech generation returns audio in the format you set with response_format:

Format	Use it for
`mp3` (default)	Playback in browsers and apps, when file size matters
`opus`	Streaming and playback over limited bandwidth
`wav`	Editing, or when you need uncompressed audio in a standard file
`flac`	Lossless archiving at a smaller size than WAV
`pcm`	Raw pipelines and telephony bridges that take raw samples, with no file header

Generated speech is mono at 24 kHz. To set the format in a request, see Response formats.

Reference audio

Two features take a short recording of a voice as a reference:

Use	Format	Number and length	Details
Speaker references for diarization	The base64 encoding of an audio file, keyed by a speaker name	Up to 8 clips, 3 to 15 seconds each	Name speakers with reference clips
Voice cloning	An MP3 or WAV file, base64-encoded. A URL isn't accepted.	A few seconds to a few minutes	Prepare a reference clip

Audio in chat completions

Audio in chat completions takes the audio inline, in the message:

How you send audio	Formats	Details
An `input_audio` content part with the base64 encoding of the file		Audio in chat completions

Voice agents SDK

The Voice Agents SDK uses one audio format of its own, for input and output:

Integration	Format	Details
Custom audio interface, or audio sent manually	16-bit signed PCM, mono, 48 kHz	Custom audio
Browser	The page's media tracks: you don't handle any format	Voice agents in the browser

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