Amazon Polly vs Fish Audio TTS API

Amazon Polly

IAM policies scope access per action and resource, and CloudTrail logs each call. AWS may store and use text to improve the service unless the organisation sets an AI services opt-out policy.

Fish Audio TTS API

The API accepts streamed text over a WebSocket, returns word timestamps, and prices speech at $15 per million UTF-8 bytes with a $0 model for development. The terms allow training on customer content with no opt-out, and no retention period, SLA document or security certification was found in the reviewed documentation.

Amazon Polly

1. Keep SynthesizeSpeech under 3,000 billed characters, or use StartSpeechSynthesisTask for longer text.
2. Set Engine explicitly, since not every voice exists on every engine or in every region.
3. Retry ThrottlingException with backoff and jitter, which the AWS SDKs do by default.
4. Check the generative SSML tag list before porting neural SSML.
5. Ask for OutputFormat json with speech marks when you need word timings.

Fish Audio TTS API

1. Send the model header on every request and check its spelling. A missing or unknown value is served and billed as s2.1-pro.
2. Budget by UTF-8 bytes, not characters. Chinese, Japanese and Korean text costs about three bytes a character.
3. Retry 429 and 5xx with exponential backoff. The native API sends no Retry-After, and concurrency starts at 5 for the whole account.
4. Use [bracket] cues on the S2 family. (parenthesis) tags from s1 are read aloud as text.
5. Pass the model explicitly in the JavaScript SDK, because npm release 0.1.0 defaults to s1.