examples: add vu meter filter

examples/qmlvumeter/VUMeterFilter.cpp

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+#include "VUMeterFilter.h"
+#include <QtAV/AudioFrame.h>
+#include <cmath>
+
+VUMeterFilter::VUMeterFilter(QObject *parent)
+    : AudioFilter(parent)
+    , mLeft(0)
+    , mRight(0)
+{
+}
+
+void VUMeterFilter::process(Statistics *statistics, AudioFrame *frame)
+{
+    if (!frame)
+        return;
+    const uchar* data = frame->constBits();
+    const int s = frame->samplesPerChannel();
+    const int cn = frame->channelCount();
+    const int r = 1;
+    float level[2];
+    const AudioFormat& af = frame->format();
+    if (af.isFloat()) {
+        float max[2];
+        max[0] = max[1] = 0;
+        const float *p = (float*)data;
+        for (int i = 0; i < s; i+=cn) {
+            max[0] = qMax(max[0], qAbs(p[i]));
+            max[1] = qMax(max[1], qAbs(p[i+r]));
+        }
+        level[0] = 20.0f * log10(max[0]);
+        level[1] = 20.0f * log10(max[1]);
+    } else if (!af.isUnsigned()) {
+        const int b = af.sampleSize();
+        if (b == 2) {
+            qint16 max[2];
+            max[0] = max[1] = 0;
+            const qint16 *p = (qint16*)data;
+            for (int i = 0; i < s; i+=cn) {
+                max[0] = qMax(max[0], qAbs(p[i]));
+                max[1] = qMax(max[1], qAbs(p[i+r]));
+            }
+            level[0] = 20.0f * log10((double)max[0]/(double)INT16_MAX);
+            level[1] = 20.0f * log10((double)max[1]/(double)INT16_MAX);
+        }
+    }
+    if (!qFuzzyCompare(level[0], mLeft)) {
+        mLeft = level[0];
+        Q_EMIT leftLevelChanged(mLeft);
+    }
+    if (!qFuzzyCompare(level[1], mRight)) {
+        mRight = level[1];
+        Q_EMIT leftLevelChanged(mRight);
+    }
+}

examples/qmlvumeter/VUMeterFilter.h

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+#ifndef VUMeterFilter_H
+#define VUMeterFilter_H
+#include <QtAV/Filter.h>
+
+using namespace QtAV;
+class VUMeterFilter : public AudioFilter
+{
+    Q_OBJECT
+    Q_PROPERTY(int leftLevel READ leftLevel WRITE setLeftLevel NOTIFY leftLevelChanged)
+    Q_PROPERTY(int rightLevel READ rightLevel WRITE setRightLevel NOTIFY rightLevelChanged)
+public:
+    VUMeterFilter(QObject* parent = NULL);
+    int leftLevel() const {return mLeft;}
+    void setLeftLevel(int value) {mLeft = value;}
+    int rightLevel() const {return mRight;}
+    void setRightLevel(int value) {mRight = value;}
+Q_SIGNALS:
+    void leftLevelChanged(int value);
+    void rightLevelChanged(int value);
+protected:
+    void process(Statistics* statistics, AudioFrame* frame = 0) Q_DECL_OVERRIDE;
+private:
+    int mLeft;
+    int mRight;
+};
+
+#endif // VUMeterFilter_H

examples/qmlvumeter/main.cpp

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+#include "VUMeterFilter.h"
+
+#include <QtGui/QGuiApplication>
+#include <QQuickItem>
+#include <QtQml/QQmlEngine>
+#include <QtQml/QQmlContext>
+#include <QtQml/QQmlApplicationEngine>
+int main(int argc, char** argv)
+{
+    qmlRegisterType<VUMeterFilter>("com.qtav.vumeter", 1, 0, "VUMeterFilter");
+    QGuiApplication app(argc, argv);
+
+    QQmlApplicationEngine engine;
+    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
+
+    return app.exec();
+}

examples/qmlvumeter/main.qml

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+import QtQuick 2.6
+import QtQuick.Window 2.2
+import QtQuick.Dialogs 1.0
+import QtAV 1.7
+import com.qtav.vumeter 1.0
+Window {
+    visible: true
+    width: 640
+    height: 480
+    title: qsTr("QtAV VU Meter Filter. Press key 'O' to open a file")
+
+    VUMeterFilter {
+        id: vu
+    }
+
+    AudioFilter {
+        id: afilter
+        type: AudioFilter.UserFilter
+        userFilter: vu
+    }
+
+    Video {
+        id: video
+        autoPlay: true
+        anchors.fill: parent
+        audioFilters: [afilter]
+        Text {
+            anchors.fill: parent
+            color: "white"
+            text: "dB left=" + vu.leftLevel + " right=" + vu.rightLevel
+        }
+    }
+
+    Item {
+        anchors.fill: parent
+        focus: true
+        Keys.onPressed: {
+            switch (event.key) {
+            case Qt.Key_O:
+                fileDialog.open()
+                break
+            }
+        }
+    }
+    FileDialog {
+        id: fileDialog
+        onAccepted: video.source = fileUrl
+    }
+}

examples/qmlvumeter/qml.qrc

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+<RCC>
+    <qresource prefix="/">
+        <file>main.qml</file>
+    </qresource>
+</RCC>

examples/qmlvumeter/qmlvumeter.pro

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+TEMPLATE = app
+CONFIG -= app_bundle
+
+QT += av qml quick
+CONFIG += c++11
+
+HEADERS = VUMeterFilter.h
+SOURCES = main.cpp VUMeterFilter.cpp
+
+RESOURCES += qml.qrc
+
+# Additional import path used to resolve QML modules in Qt Creator's code model
+QML_IMPORT_PATH =
+
+# Additional import path used to resolve QML modules just for Qt Quick Designer
+QML_DESIGNER_IMPORT_PATH =
+
+# The following define makes your compiler emit warnings if you use
+# any feature of Qt which as been marked deprecated (the exact warnings
+# depend on your compiler). Please consult the documentation of the
+# deprecated API in order to know how to port your code away from it.
+DEFINES += QT_DEPRECATED_WARNINGS
+
+# You can also make your code fail to compile if you use deprecated APIs.
+# In order to do so, uncomment the following line.
+# You can also select to disable deprecated APIs only up to a certain version of Qt.
+#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
+
+# Default rules for deployment.
+qnx: target.path = /tmp/$${TARGET}/bin
+else: unix:!android: target.path = /opt/$${TARGET}/bin
+!isEmpty(target.path): INSTALLS += target