Voice GenerationText to Speech

Streaming (HTTP)

Use the streaming endpoint to start playback as audio is generated. Responses are chunked WAV data so you can progressively feed a player while long-form synthesis completes.

See the streaming demo project for a full reference implementation.

Careful: Streaming requests target dedicated synthesis hosts (see your streaming endpoint in the dashboard). Do not send them to app.resemble.ai.

Endpoint

POST https://f.cluster.resemble.ai/stream

Request Body

FieldTypeRequiredDescription
voice_uuidstringYesVoice to synthesize.
datastringYesText or SSML to synthesize (≤ 2,000 characters; partial SSML support).
project_uuidstringNoProject that will own the generated clip.
precisionstringNoOne of PCM_32, PCM_24, PCM_16, or MULAW. Defaults to PCM_32.
sample_ratenumberNoOne of 8000, 16000, 22050, 32000, 44100, or 48000. Defaults to 48000.
use_hdbooleanNoEnables higher-definition synthesis with a small latency trade-off. Defaults to false.

Response

The response is a single-channel PCM WAV stream. The first bytes include metadata describing duration and timestamps before audio frames arrive.

Working with the Stream

  1. Read the first chunk to obtain metadata such as duration, grapheme timestamps, and phoneme timestamps.
  2. Continue reading chunks and feed them to your playback pipeline.
  3. Handle the Content-Encoding header if you requested compression.

Try it – Issue a streaming request and pipe the response to a file:

$curl --output - "https://f.cluster.resemble.ai/stream" \
>  -H "Authorization: Bearer YOUR_API_TOKEN" \
>  -H "Content-Type: application/json" \
>  --data '{
>    "voice_uuid": "YOUR_VOICE_UUID",
>    "data": "Streaming helps deliver synthesized audio before it is finished.",
>    "precision": "PCM_16"
>  }' \
>| ffplay -

WAV Metadata Layout

Resemble annotates WAV headers to expose timing data without additional requests.

  • File-level metadata in the RIFF and fmt chunks
  • Grapheme and phoneme cue points in cue, list, and ltxt chunks
  • PCM audio bytes in the data chunk

Header & Format Chunks

SizeDescriptionValue
4RIFF ID"RIFF"
4Remaining file size(file size) - 8
4RIFF type"WAVE"
4Format chunk ID"fmt "
4Chunk data size16
2Compression code1 (PCM)
2Number of channels1
4Sample rate8000–48000
4Byte rate16000–96000
2Block align2
2Bits per sample16

Older models may report the file size as 0xFFFFFFFF. Contact support to upgrade if you see this value.

Cue, List, and LTXT Chunks

  • cue chunk lists offsets for grapheme and phoneme boundaries.
  • list chunk (type adtl) groups label data.
  • Each ltxt chunk pairs a cue ID with either a grapheme ("grph") or phoneme ("phon") label and duration (in samples).

When reading ltxt chunks, align to 2-byte boundaries. If text_length is odd, skip an additional byte before the next chunk.

Data Chunk

SizeDescriptionValue
4Data chunk ID"data"
4Remaining byteswav_length * 2

After the header metadata, the stream consists of PCM16 samples that you can decode on the fly.