Speak the usual way during calls rather than through low-latency audio

[aaron-gh]

With low-latency audio on, Backtalk fell back from the selected text-to-speech engine to Google Speech Services when a call started in Aira. The call's audio mode (MODE_IN_COMMUNICATION) is set before its microphone recording starts, so the microphone check did not catch it. The engines then said nothing about the first speech after the audio mode changed, the hang check at ENGINE_HANG_MS (3 s) counted them as hung, and Backtalk switched engines twice in 5 s. The reporter's logcat shows the two engine switches at those times. It does not contain Backtalk's own "said nothing … hung" line, so this cause is inferred from timing.

• Speech uses the engine's own playback, not low-latency audio, while the audio mode is MODE_IN_CALL or MODE_IN_COMMUNICATION.
• The engine hang check only watches speech that uses low-latency audio. Before, it also watched speech that had fallen back to normal playback.

Limitations:

• Speech that low-latency audio started before a call began can still hit the hang check if the engine stays silent for 3 s.