SSML

SSML (Speech Synthesis Markup Language) is an XML-based W3C standard for controlling synthetic speech output characteristics (e.g., pitch, rate, volume) in text-to-speech (TTS) applications.

SSML is the XML-based markup language, a W3C Recommendation, designed to provide authors with a standard, platform-independent method for controlling synthetic speech generation in web and voice applications. It uses elements like `<prosody>` and `<break>` to precisely manage speech output aspects: this includes pronunciation, inserting specific pauses, selecting a voice, and adjusting prosody (pitch, volume, and speaking rate). This granular control is essential for producing high-quality, natural-sounding audio for systems such as interactive voice response (IVR), audiobooks, and virtual assistants (Amazon Alexa, Google Assistant).

https://www.w3.org/TR/speech-synthesis/