Player: be smooth when play stops

- free pulseaudio playback after a delay, to permit buffered sound to play

- do zero crossing in playing signal to detect the right moment to stop or
  update frequency

src/TunerWorker.cpp

@@ -55,6 +55,7 @@ static void blank_prevent(bool prevent)
 }
 
 TunerWorker::TunerWorker() :
+	play_stop_counter(0),
 	running(false),
 	playing(false),
 	quit(false),
@@ -92,8 +93,15 @@ void TunerWorker::SetPlaying(bool p)
 	cerr << __func__ << " " << p << endl;
 	if (p == playing) return;
 	mutex.lock();
-	playing = p;
-	if (p) condition.wakeOne();
+	if (p) {
+		playing = p;
+		play_stop_counter = 0;
+		condition.wakeOne();
+	}
+	else {
+		// stop after a frame
+		play_stop_counter = 1;
+	}
 	mutex.unlock();
 }
 
@@ -167,21 +175,27 @@ void TunerWorker::Entry()
 	while (1) {
 
 		mutex.lock();
+		// stop playing after a frame
+		if (play_stop_counter >= 2) playing = false;
+
 		// free pulseaudio if not running
 		if (!running && p_record) {
 			pa_simple_free(p_record);
-			p_record = NULL;
-		}
-		if (!playing && p_play) {
-			pa_simple_free(p_play);
-			p_play = NULL;
+			p_record = nullptr;
 		}
+		// free playing after a delay of inactivity to avoid clac
 
 		// wait for running
 		if (!running && !playing) {
 			blank_prevent(false);
+			bool waked;
 			while (!running && !playing && !quit) {
-				condition.wait(&mutex);
+				waked = condition.wait(&mutex, p_play ? 1000000 : ULONG_MAX);
+				// free playing now
+				if (!waked && p_play) {
+					pa_simple_free(p_play);
+					p_play = nullptr;
+				}
 			}
 			cerr << "wake-up" << endl;
 			nb_sample_running = 0;
@@ -277,11 +291,15 @@ void TunerWorker::Entry()
 				player->SetFreq(pitchDetection->GetNoteFreq(result.note, result.octave));
 			}
 
-			player->WriteAudio(buffer, nbSampleBuffer);
+			const int stop_counter = play_stop_counter;
+
+			player->WriteAudio(buffer, nbSampleBuffer, stop_counter > 0);
 			if (pa_simple_write(p_play, buffer, nbSampleBuffer << 1, nullptr) < 0) {
 				cerr << "audio write failed" << endl;
 			}
-			//else cout << "audio written" << endl;
+
+			if (stop_counter) play_stop_counter = stop_counter + 1;
+
 		} // playing
 
 		// prevent screen blanking

src/TunerWorker.hpp

@@ -45,6 +45,7 @@ class TunerWorker : public QObject {
 	QMutex mutex;
 	QWaitCondition condition;
 
+	int play_stop_counter;
 	bool running, playing, quit;
 
 	// to update vars

src/audio/FreqPlayer.cpp

@@ -35,6 +35,7 @@ template<typename sample_t> FreqPlayer<sample_t>::FreqPlayer(int _rate):
 template<typename sample_t> void FreqPlayer<sample_t>::Reset()
 {
 	n_frame = 0;
+	last_frame = 0;
 	if (k_update != -1) {
 		k = k_update;
 		k_update = -1;
@@ -62,21 +63,7 @@ template<> double FreqPlayer<double>::max() { return 1; }
 
 template<typename sample_t> double FreqPlayer<sample_t>::radius()
 {
-	double ret = (double) (n_frame++) * k;
-
-	/* to update frequency factor, wait current radius to go to beginning
-	 * in interval [0, 2PI]
-	 */
-	if (k_update != -1) {
-		double a = fmod(ret, M_PI * 1);
-		double b = fmod(n_frame * k, M_PI * 2);
-		if (b < a) { // next frame go back to beginning of circle
-			n_frame = 0;
-			k = k_update;
-			k_update = -1;
-		}
-	}
-	return ret;
+	return (double) (n_frame++) * k;
 }
 
 template<typename sample_t> sample_t FreqPlayer<sample_t>::AudioFrame()
@@ -90,9 +77,34 @@ template<typename sample_t> sample_t FreqPlayer<sample_t>::AudioFrame()
 	}
 }
 
-template<typename sample_t> void FreqPlayer<sample_t>::WriteAudio(sample_t *out, int nb_frame)
+template<typename sample_t> void FreqPlayer<sample_t>::WriteAudio(sample_t *out, int nb_frame, bool stop)
 {
-	while (nb_frame--) *out++ = AudioFrame();
+	sample_t v;
+	const bool to_update = (k_update != -1) || stop;
+
+	while (nb_frame--) {
+		v = AudioFrame();
+		if (to_update && (v >= 0 && last_frame < 0)) {
+			// zero cross. update now.
+			if (k_update != -1) {
+				// update frequency
+				n_frame = 0;
+				k = k_update;
+				k_update = -1;
+				v = AudioFrame();
+			}
+			else if (stop) {
+				std::cerr << "stop audio" << std::endl;
+				// finish with 0s
+				*out++ = 0;
+				while (nb_frame--) *out++ = 0;
+				last_frame = 0;
+				return;
+			}
+		}
+		*out++ = v;
+		last_frame = v;
+	}
 }
 
 // instanciation for int16

src/audio/FreqPlayer.hpp

@@ -42,6 +42,8 @@ template<typename sample_t> class FreqPlayer {
 	WAVEFORM waveform;
 	/// pre computed factor
 	double k, k_update;
+	// last frame written
+	sample_t last_frame;
 
 	/// return k computed
 	double K() const;
@@ -59,7 +61,7 @@ template<typename sample_t> class FreqPlayer {
 	/// get next audio frame
 	inline sample_t AudioFrame();
 	/// write audio buffer
-	void WriteAudio(sample_t *out, int nb_frame);
+	void WriteAudio(sample_t *out, int nb_frame, bool stop = false);
 	/// set current frequency
 	void SetFreq(double freq);
 	/// set current volume