Audio formats

Describe the audio you send in the init body. The API reads your stream with these values: they must match it.

field	values	default
encoding	wav/pcm (linear PCM), wav/alaw, wav/ulaw (G.711, telephony)	wav/pcm
bit_depth	8, 16, 24, 32; wav/alaw and wav/ulaw are 8-bit	16
sample_rate	8000, 16000, 32000, 44100, 48000	16000
channels	1 to 8	1

Send the samples raw, without a WAV header: little-endian, channels interleaved.

{ "encoding": "wav/ulaw", "sample_rate": 8000, "bit_depth": 8, "channels": 2 }

Sending the audio

• Binary frames (recommended): the bytes as they are.
• JSON: {"type": "audio_chunk", "data": {"chunk": "<base64>"}}, a third larger.

Any chunk size works. 100 ms per chunk is a good default: smaller chunks add overhead, larger ones delay the transcripts. Send the audio as it is captured.

Several channels

Each channel is transcribed on its own: utterances carry their channel (from 0), and utterance ids start with it (01_00000004). Put each party of a call on its own channel to know who said what without diarization, and with exact timing when they talk over each other.

Acknowledgments

With receive_acknowledgments (on by default), the server acknowledges your audio once it is transcribed, with audio_chunk messages whose byte_range counts the bytes since the start of the session. Keep the audio until it is acknowledged to resend it after a network drop (Reconnections).