Amazon Polly vs Azure AI Speech text-to-speech

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.

Azure AI Speech text-to-speech

Real-time synthesis keeps neither the input text nor the output audio. An Azure subscription needs a card, even for the free F0 tier.

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.

Azure AI Speech text-to-speech

1. Send SSML with <speak> and <voice>, and set X-Microsoft-OutputFormat and User-Agent.
2. On 429 retry with backoff, and try the voice's home region or another region rather than asking for more quota.
3. Keep each real-time request under 10 minutes of audio, or use batch synthesis.
4. Use Entra ID tokens instead of resource keys where the agent runs inside Azure.
5. Cache the voice list per region, since it returns hundreds of entries at once.