time_stretch: Simplify audio stretcher

src/audio_core/dsp_interface.cpp

@@ -15,6 +15,7 @@ DspInterface::DspInterface() = default;
 DspInterface::~DspInterface() = default;
 
 void DspInterface::SetSink(const std::string& sink_id, const std::string& audio_device) {
+    sink.reset();
     const SinkDetails& sink_details = GetSinkDetails(sink_id);
     sink = sink_details.factory(audio_device);
     sink->SetCallback(
@@ -32,7 +33,7 @@ void DspInterface::EnableStretching(bool enable) {
         return;
 
     if (!enable) {
-        FlushResidualStretcherAudio();
+        flushing_time_stretcher = true;
     }
     perform_time_stretching = enable;
 }
@@ -51,17 +52,27 @@ void DspInterface::OutputFrame(StereoFrame16& frame) {
     fifo.Push(frame.data(), frame.size());
 }
 
-void DspInterface::FlushResidualStretcherAudio() {}
-
-void DspInterface::OutputCallback(s16* buffer, size_t num_frames) {
-    const size_t frames_written = fifo.Pop(buffer, num_frames);
+void DspInterface::OutputCallback(s16* buffer, std::size_t num_frames) {
+    std::size_t frames_written;
+    if (perform_time_stretching) {
+        const std::vector<s16> in{fifo.Pop()};
+        const std::size_t num_in{in.size() / 2};
+        frames_written = time_stretcher.Process(in.data(), num_in, buffer, num_frames);
+    } else if (flushing_time_stretcher) {
+        time_stretcher.Flush();
+        frames_written = time_stretcher.Process(nullptr, 0, buffer, num_frames);
+        frames_written += fifo.Pop(buffer, num_frames - frames_written);
+        flushing_time_stretcher = false;
+    } else {
+        frames_written = fifo.Pop(buffer, num_frames);
+    }
 
     if (frames_written > 0) {
         std::memcpy(&last_frame[0], buffer + 2 * (frames_written - 1), 2 * sizeof(s16));
     }
 
     // Hold last emitted frame; this prevents popping.
-    for (size_t i = frames_written; i < num_frames; i++) {
+    for (std::size_t i = frames_written; i < num_frames; i++) {
         std::memcpy(buffer + 2 * i, &last_frame[0], 2 * sizeof(s16));
     }
 }