Specifically, firstly, the disable_standby_mode_silence_threshold, which is the
amount of audio in the output device's hardware buffer. It should normally
be close to the value givein in the audio_backend_buffer_desired_length_in_seconds
setting. If it drops to this value, silence is added to the buffer to prevent
the output device from becoming idle.
Secondly, the disable_standby_mode_silence_scan_interval is the time between checks
of the output device's hardware buffer.
The code for generating frames of possibly-dithered silence has been simplified.
Mike Brady
a8faacd3fc