> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.kotoba.tech/overview/audio-formats/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.kotoba.tech/_mcp/server.

# Audio formats

The ASR, STS, and TTS APIs all speak JSON over WebSocket, and audio
payloads are Base64-encoded inside event bodies.

## Input audio (ASR / STS)

| Format     | Description                             |
| ---------- | --------------------------------------- |
| `pcm16`    | 16-bit signed little-endian PCM         |
| `float32`  | 32-bit IEEE float PCM                   |
| `twilio`   | μ-law 8 kHz mono (Twilio Media Streams) |
| `ogg/opus` | Ogg-wrapped Opus                        |

Sample rate defaults to **24,000 Hz** and mono (`1` channel). You can
change both via the session update event.

## Output audio (STS / TTS)

| Format    | Description                             |
| --------- | --------------------------------------- |
| `pcm16`   | 16-bit signed little-endian PCM         |
| `float32` | 32-bit IEEE float PCM                   |
| `twilio`  | μ-law 8 kHz mono (Twilio Media Streams) |

## Chunk size

Each `input_audio_buffer.append` event can carry up to **1 MiB**
(approximately 10 seconds at the default sample rate). For most
real-time applications, 20–40 ms chunks work well.

> Supported input and output encodings.