Long text

1. Use the SDKs. Both the Python and TypeScript SDKs automatically split long input, generate each segment, and merge the audio for you. You get one final clip back even if the input was 2,000 characters.
2. Chunk yourself. If you call the REST API directly, split the text on sentence boundaries and concatenate the resulting audio.

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The 300-character limit, at a glance

# Python — pass maxTextLength via SDK options
# (the default is 300; lower it to chunk earlier)

// TypeScript — pass maxTextLength in the options object
const response = await client.textToSpeech.createSpeech(
  { voiceId, apiConvertTextToSpeechUsingCharacterRequest: { text, language: "en" } },
  { maxTextLength: 250 },
);

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SDK auto-chunking, end to end

import os
from supertone import Supertone

VOICE_ID = "20160a4c5ba38967330c84"  # replace with your voice ID

LONG_TEXT = (
    "Once upon a time, in a faraway land, there lived a quiet librarian "
    "who collected stories of forgotten kingdoms. Every evening she would "
    "open a leather-bound notebook and continue writing the next chapter "
    "of a tale she had been telling herself for years. ...continue with "
    "many more sentences spanning over 300 characters..."
)

with Supertone(api_key=os.environ["SUPERTONE_API_KEY"]) as client:
    response = client.text_to_speech.create_speech(
        voice_id=VOICE_ID,
        text=LONG_TEXT,
        language="en",
    )

    with open("narration.wav", "wb") as f:
        f.write(response.result.read())

import { Supertone } from "@supertone/supertone";
import * as fs from "node:fs";

const VOICE_ID = "20160a4c5ba38967330c84"; // replace with your voice ID

const LONG_TEXT = `
  Once upon a time, in a faraway land, there lived a quiet librarian
  who collected stories of forgotten kingdoms. Every evening she would
  open a leather-bound notebook and continue writing the next chapter
  of a tale she had been telling herself for years. ...continue with
  many more sentences spanning over 300 characters...
`.trim();

const client = new Supertone({ apiKey: process.env.SUPERTONE_API_KEY });

const response = await client.textToSpeech.createSpeech({
  voiceId: VOICE_ID,
  apiConvertTextToSpeechUsingCharacterRequest: {
    text: LONG_TEXT,
    language: "en",
  },
});

if (response.result instanceof Uint8Array) {
  fs.writeFileSync("narration.wav", response.result);
} else if (response.result && "getReader" in response.result) {
  const reader = (response.result as ReadableStream<Uint8Array>).getReader();
  const chunks: Uint8Array[] = [];
  while (true) {
    const { done, value } = await reader.read();
    if (done) break;
    if (value) chunks.push(value);
  }
  fs.writeFileSync("narration.wav", Buffer.concat(chunks));
}

​

Streaming long text

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Chunking yourself (cURL or raw HTTP)

1. Split on sentence-ending punctuation (., !, ?, 。, ？).
2. If a sentence is still over 300 characters, split on commas, then on word boundaries.
3. For each segment, call POST /v1/text-to-speech/{voice_id} and append the returned audio to your output file.
4. For WAV concatenation, strip the WAV header (first 44 bytes) from every segment after the first so the final file plays as one clip.

# Pseudo-shell: split a script and concatenate WAV chunks
VOICE_ID="20160a4c5ba38967330c84"

split_into_sentences "$INPUT_TEXT" > sentences.txt
while read -r line; do
  curl -s -X POST "https://supertoneapi.com/v1/text-to-speech/$VOICE_ID" \
    -H "x-sup-api-key: $SUPERTONE_API_KEY" \
    -H "Content-Type: application/json" \
    -d "{\"text\": \"$line\", \"language\": \"en\"}" \
    >> raw_chunks.bin
done < sentences.txt
# Then merge with your audio tooling (ffmpeg, etc.) and re-attach a single WAV header.

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Tips

• Punctuation matters. Auto-chunking prefers sentence boundaries. Well-punctuated input produces cleaner cuts and more natural transitions.
• Estimate cost first. predict_duration doesn’t auto-chunk, but you can split text yourself and sum durations to estimate total credits.
• Watch rate limits. A single long input becomes multiple TTS requests — track your account’s rate limits and consider throttling in your own caller.

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