diff audio/TimeStretchWrapper.h @ 738:48001ed9143b audio-source-refactor

Introduce TimeStretchWrapper; some work towards making the AudioCallbackPlaySource not actually try to be an ApplicationPlaybackSource itself but only return one that is constructed from wrappers that it controls the lifespan of

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/audio/TimeStretchWrapper.h	Wed Mar 18 12:51:41 2020 +0000
@@ -0,0 +1,108 @@
+/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
+
+/*
+    Sonic Visualiser
+    An audio file viewer and annotation editor.
+    Centre for Digital Music, Queen Mary, University of London.
+    
+    This program is free software; you can redistribute it and/or
+    modify it under the terms of the GNU General Public License as
+    published by the Free Software Foundation; either version 2 of the
+    License, or (at your option) any later version.  See the file
+    COPYING included with this distribution for more information.
+*/
+
+#ifndef SV_TIME_STRETCH_WRAPPER_H
+#define SV_TIME_STRETCH_WRAPPER_H
+
+#include "bqaudioio/ApplicationPlaybackSource.h"
+
+#include "base/BaseTypes.h"
+
+#include <vector>
+#include <mutex>
+
+namespace RubberBand {
+    class RubberBandStretcher;
+}
+
+/**
+ * A breakfastquay::ApplicationPlaybackSource wrapper that implements
+ * time-stretching using Rubber Band. Note that the stretcher is
+ * bypassed entirely when a ratio of 1.0 is set; this means it's
+ * (almost) free to use one of these wrappers normally, but it also
+ * means you can't switch from 1.0 to another ratio (or back again)
+ * without some audible artifacts.
+ *
+ * This is real-time safe while the ratio is fixed, and may perform
+ * reallocations when the ratio changes.
+ */
+class TimeStretchWrapper : public breakfastquay::ApplicationPlaybackSource
+{
+public:
+    /**
+     * Create a wrapper around the given ApplicationPlaybackSource,
+     * implementing another ApplicationPlaybackSource interface that
+     * draws from the same source data but with a time-stretcher
+     * optionally applied.
+     *
+     * The wrapper does not take ownership of the wrapped
+     * ApplicationPlaybackSource, whose lifespan must exceed that of
+     * this object.    
+     */
+    TimeStretchWrapper(ApplicationPlaybackSource *source);
+    ~TimeStretchWrapper();
+
+    /**
+     * Set a time stretch factor, i.e. playback speed, where 1.0 is
+     * normal speed
+     */
+    void setTimeStretchRatio(double ratio);
+
+    /**
+     * Clear stretcher buffers.
+     */
+    void reset();
+
+    // These functions are passed through to the wrapped
+    // ApplicationPlaybackSource
+    
+    std::string getClientName() const override;
+    int getApplicationSampleRate() const override;
+    int getApplicationChannelCount() const override;
+
+    void setSystemPlaybackBlockSize(int) override;
+    void setSystemPlaybackSampleRate(int) override;
+    void setSystemPlaybackChannelCount(int) override;
+    void setSystemPlaybackLatency(int) override;
+
+    void setOutputLevels(float peakLeft, float peakRight) override;
+    void audioProcessingOverload() override;
+
+    /** 
+     * Request some samples from the wrapped
+     * ApplicationPlaybackSource, time-stretch if appropriate, and
+     * return them to the target
+     */
+    int getSourceSamples(float *const *samples, int nchannels, int nframes)
+        override;
+
+private:
+    ApplicationPlaybackSource *m_source;
+    RubberBand::RubberBandStretcher *m_stretcher;
+    double m_timeRatio;
+    std::vector<std::vector<float>> m_inputs;
+    std::mutex m_mutex;
+    sv_frame_t m_stretcherInputSize;
+    int m_channelCount;
+    sv_samplerate_t m_sampleRate;
+
+    void checkStretcher(); // call without m_mutex held
+    
+    TimeStretchWrapper(const TimeStretchWrapper &)=delete;
+    TimeStretchWrapper &operator=(const TimeStretchWrapper &)=delete;
+};
+
+#endif
+
+