Attempt implementing offline rendering from the plugin but not going so great. Looks like the StretchAudioSource doesn't really work that robustly...

Source/PS_Source/globals.h

@@ -294,3 +294,11 @@ inline bool is_in_range(T val, T start, T end)
 {
 	return val >= start && val <= end;
 }
+
+inline void sanitizeTimeRange(double& t0, double& t1)
+{
+	if (t0 > t1)
+		std::swap(t0, t1);
+	if (t1 - t0 < 0.001)
+		t1 = t0 + 0.001;
+}

Source/PluginEditor.cpp

@@ -358,6 +358,7 @@ void PaulstretchpluginAudioProcessorEditor::showSettingsMenu()
 	menu.addItem(6, "Dump preset to clipboard", true, false);
 #endif
 	menu.addItem(7, "Show technical info", true, processor.m_show_technical_info);
+	menu.addItem(8, "Offline render...", true, false);
 	int r = menu.show();
 	if (r >= 200 && r < 210)
 	{
@@ -415,6 +416,10 @@ void PaulstretchpluginAudioProcessorEditor::showSettingsMenu()
 		toggleBool(processor.m_show_technical_info);
 		processor.m_propsfile->m_props_file->setValue("showtechnicalinfo", processor.m_show_technical_info);
 	}
+	if (r == 8)
+	{
+		processor.offlineRender(File("C:\\MusicAudio\\sourcesamples\\paultesmaus\\plugin_offline_test\\out.wav"));
+	}
 }
 
 WaveformComponent::WaveformComponent(AudioFormatManager* afm, AudioThumbnail* thumb)

Source/PluginProcessor.cpp

@@ -411,9 +411,60 @@ void PaulstretchpluginAudioProcessor::updateStretchParametersFromPluginParameter
 	pars.tonal_vs_noise.preserve = *getFloatParameter(cpi_tonalvsnoisepreserve);
 }
 
+String PaulstretchpluginAudioProcessor::offlineRender(File outputfile)
+{
+	File outputfiletouse = outputfile.getNonexistentSibling();
+	int numoutchans = *getIntParameter(cpi_num_outchans);
+	auto ss = std::make_shared<StretchAudioSource>(numoutchans,m_afm);
+	int blocksize = 2048;
+	int64_t outlen = 10 * getSampleRateChecked();
+	int64_t outcounter = 0;
+	ss->setFFTSize(m_fft_size_to_use);
+	ss->setAudioFile(m_current_file);
+	ProcessParameters renderpars;
+	updateStretchParametersFromPluginParameters(renderpars);
+	ss->setProcessParameters(&renderpars);
+	double t0 = *getFloatParameter(cpi_soundstart);
+	double t1 = *getFloatParameter(cpi_soundend);
+	sanitizeTimeRange(t0, t1);
+	ss->setRate(*getFloatParameter(cpi_stretchamount));
+	ss->setPlayRange({ t0,t1 }, true);
+	ss->setLoopingEnabled(true);
+	ss->setNumOutChannels(numoutchans);
+	ss->setFFTWindowingType(1);
+	ss->setPreviewDry(true);
+	ss->setOnsetDetection(*getFloatParameter(cpi_onsetdetection));
+	ss->setLoopXFadeLength(*getFloatParameter(cpi_loopxfadelen));
+	ss->setFreezing(getParameter(cpi_freeze));
+	ss->setPaused(getParameter(cpi_pause_enabled));
+	ss->prepareToPlay(blocksize, getSampleRateChecked());
+	AudioBuffer<float> renderbuffer(numoutchans, blocksize);
+	
+	WavAudioFormat wavformat;
+	FileOutputStream* outstream = outputfiletouse.createOutputStream();
+	if (outstream == nullptr)
+		return "Could not create output file";
+	auto writer = wavformat.createWriterFor(outstream, getSampleRateChecked(), numoutchans, 32, StringPairArray(), 0);
+	if (writer == nullptr)
+	{
+		delete outstream;
+		return "Could not create WAV writer";
+	}
+	AudioSourceChannelInfo asci(renderbuffer);
+	while (outcounter < outlen)
+	{
+		ss->setMainVolume(*getFloatParameter(cpi_main_volume));
+		ss->getNextAudioBlock(asci);
+		writer->writeFromAudioSampleBuffer(renderbuffer,0,blocksize);
+		outcounter += blocksize;
+	}
+	delete writer;
+	return "Rendered OK";
+}
+
 double PaulstretchpluginAudioProcessor::getSampleRateChecked()
 {
-	if (m_cur_sr < 1.0)
+	if (m_cur_sr < 1.0 || m_cur_sr>1000000.0)
 		return 44100.0;
 	return m_cur_sr;
 }
@@ -503,14 +554,6 @@ void copyAudioBufferWrappingPosition(const AudioBuffer<float>& src, AudioBuffer<
 	}
 }
 
-inline void sanitizeTimeRange(double& t0, double& t1)
-{
-	if (t0 > t1)
-		std::swap(t0, t1);
-	if (t1 - t0 < 0.001)
-		t1 = t0 + 0.001;
-}
-
 void PaulstretchpluginAudioProcessor::processBlock (AudioSampleBuffer& buffer, MidiBuffer& midiMessages)
 {
 	ScopedLock locker(m_cs);

Source/PluginProcessor.h

@@ -161,6 +161,7 @@ public:
 	bool m_load_file_with_state = true;
 	ValueTree getStateTree(bool ignoreoptions, bool ignorefile);
 	void setStateFromTree(ValueTree tree);
+	String offlineRender(File outputfile);
 	bool m_state_dirty = false;
 	std::unique_ptr<AudioThumbnail> m_thumb;
 	bool m_show_technical_info = false;
@@ -207,6 +208,7 @@ private:
 	void setParameters(const std::vector<double>& pars);
 	float m_cur_playrangeoffset = 0.0;
 	void updateStretchParametersFromPluginParameters(ProcessParameters& pars);
+	
 	//==============================================================================
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (PaulstretchpluginAudioProcessor)
 };