If you're looking for a powerful Text-to-Speech API for your educational app, Narration Box is a great option. It supports more than 140 languages and accents, with a lot of options for fine-tuning voice inflection, rate and pitch, and for customizing pronunciation. The platform also comes with a block-based interface that's easy to use and a library of 700+ AI narrators, so it's great for high-quality voiceovers for e-learning content.
Another good option is Unreal Speech, which offers high-quality speech synthesis at a lower price. It can export in standard formats like MP3 and PCM µ-law with a variety of bitrate options from 16k to 192k, and you can control the speed and pitch of the generated speech. The API also has live demo testing and code samples in Python, so it's easy to get started in your educational app.