VoiceScroll uses on-device speech recognition to follow your position in the script and adjust the scroll speed. It works offline and doesn't require an account. Speech and scripts stay on the device.
Scripts up to 300 characters are free. Longer scripts require a one-time purchase; there's no subscription. It's available on iOS and Android and currently supports 22 languages.
I'm happy to go into more detail about how the script matching works.