Android O New Texttospeech Onrangestart() Callback

The new callback function onRangeStart() of TTS UtteranceProgressListener would let us e.g. highlight individual words of a longer phrase, as it's spoken by the TTS engine. The cal

Solution 1:

Google is still not documenting this feature and the latest response to the issue filed in their tracker is "We've deferred this to a future release, but leaving this open for now."

Meantime by implementing onRangeStart() callback in my TTS app and make it show debug output, I see that that the "ranges" are simply words. I see this callback hit when using English voices from Google TTS only, no other TTS voices from Google or other companies that I tried so far, implement this yet. For example, reading aloud a sentence: "This is a sentence to read aloud." produces the following output in onRangeStart():

onRangeStart(avar-1) start=0, end=4, frame=275         (This)
onRangeStart(avar-1) start=5, end=7, frame=3575        (is)
onRangeStart(avar-1) start=8, end=9, frame=6270        (a)
onRangeStart(avar-1) start=10, end=18, frame=7810      (sentence)
onRangeStart(avar-1) start=19, end=21, frame=18535     (to)
onRangeStart(avar-1) start=22, end=26, frame=21285     (read)
onRangeStart(avar-1) start=27, end=32, frame=25795     (aloud)

It would be helpful if someone from Google told us officially that "ranges" are simply words, at least for now.