pub type OnMarkCallback<'a> = &'a mut dyn FnMut(&str, f32, f32, i32);Expand description
Callback for SSML mark/bookmark events.
Signature: (name, start_sec, end_sec, char_offset)
char_offset is -1 when the engine doesn’t report it. Engines that
estimated) audio position; consumers map it to their bookmark event
(SAPI SPEI_TTS_BOOKMARK, SSIP index marks).