Clarify API/docs by introducing the audio "frame", and add helpers.

The frame is the interleaved set of one sample for each channel.  Add
some docs and some methods that make working with samples a bit more
convenient.

Adjusted QAudioBuffer to use these helper functions and terminology.

Change-Id: I96db48e659561972d6de2aa19893d29f9a828cd3
Reviewed-by: Dmytro Poplavskiy <dmytro.poplavskiy@nokia.com>

5 files changed, 206 insertions, 71 deletions

diff --git a/src/multimedia/audio/qaudiobuffer.cpp b/src/multimedia/audio/qaudiobuffer.cpp
index bde04501f..299a610fa 100644
--- a/src/multimedia/audio/qaudiobuffer.cpp
+++ b/src/multimedia/audio/qaudiobuffer.cpp
@@ -106,18 +106,18 @@ public:
 // Private class to go in .cpp file
 class QMemoryAudioBufferProvider : public QAbstractAudioBuffer {
 public:
-    QMemoryAudioBufferProvider(const void *data, int sampleCount, const QAudioFormat &format, qint64 startTime)
+    QMemoryAudioBufferProvider(const void *data, int frameCount, const QAudioFormat &format, qint64 startTime)
         : mStartTime(startTime)
-        , mSampleCount(sampleCount)
+        , mFrameCount(frameCount)
         , mFormat(format)
     {
-        int numBytes = (sampleCount * format.sampleSize()) / 8;
+        int numBytes = format.bytesForFrames(frameCount);
         if (numBytes > 0) {
             mBuffer = malloc(numBytes);
             if (!mBuffer) {
                 // OOM, if that's likely
                 mStartTime = -1;
-                mSampleCount = 0;
+                mFrameCount = 0;
                 mFormat = QAudioFormat();
             } else {
                 // Allocated, see if we have data to copy
@@ -149,19 +149,19 @@ public:
     void release() {delete this;}
     QAudioFormat format() const {return mFormat;}
     qint64 startTime() const {return mStartTime;}
-    int sampleCount() const {return mSampleCount;}
+    int frameCount() const {return mFrameCount;}
 
     void *constData() const {return mBuffer;}
 
     void *writableData() {return mBuffer;}
     QAbstractAudioBuffer *clone() const
     {
-        return new QMemoryAudioBufferProvider(mBuffer, mSampleCount, mFormat, mStartTime);
+        return new QMemoryAudioBufferProvider(mBuffer, mFrameCount, mFormat, mStartTime);
     }
 
     void *mBuffer;
     qint64 mStartTime;
-    int mSampleCount;
+    int mFrameCount;
     QAudioFormat mFormat;
 };
 
@@ -176,7 +176,7 @@ QAudioBufferPrivate *QAudioBufferPrivate::clone()
         QAbstractAudioBuffer *abuf = mProvider->clone();
 
         if (!abuf) {
-            abuf = new QMemoryAudioBufferProvider(mProvider->constData(), mProvider->sampleCount(), mProvider->format(), mProvider->startTime());
+            abuf = new QMemoryAudioBufferProvider(mProvider->constData(), mProvider->frameCount(), mProvider->format(), mProvider->startTime());
         }
 
         if (abuf) {
@@ -236,7 +236,7 @@ QAudioBuffer::QAudioBuffer(const QAudioBuffer &other)
     and sizes of the samples are interpreted from the \a data.
 
     If the supplied \a data is not an integer multiple of the
-    calculated sample size, the excess data will not be used.
+    calculated frame size, the excess data will not be used.
 
     This audio buffer will copy the contents of \a data.
 
@@ -247,25 +247,25 @@ QAudioBuffer::QAudioBuffer(const QAudioBuffer &other)
 QAudioBuffer::QAudioBuffer(const QByteArray &data, const QAudioFormat &format, qint64 startTime)
 {
     if (format.isValid()) {
-        int sampleCount = (data.size() * 8) / format.sampleSize(); // truncate
-        d = new QAudioBufferPrivate(new QMemoryAudioBufferProvider(data.constData(), sampleCount, format, startTime));
+        int frameCount = format.framesForBytes(data.size());
+        d = new QAudioBufferPrivate(new QMemoryAudioBufferProvider(data.constData(), frameCount, format, startTime));
     } else
         d = 0;
 }
 
 /*!
-    Creates a new audio buffer with space for \a numSamples samples of
-    the given \a format.  The samples will be initialized to the default
-    for the format.
+    Creates a new audio buffer with space for \a numFrames frames of
+    the given \a format.  The individual samples will be initialized
+    to the default for the format.
 
     \a startTime (in microseconds) indicates when this buffer
     starts in the stream.
     If this buffer is not part of a stream, set it to -1.
  */
-QAudioBuffer::QAudioBuffer(int numSamples, const QAudioFormat &format, qint64 startTime)
+QAudioBuffer::QAudioBuffer(int numFrames, const QAudioFormat &format, qint64 startTime)
 {
     if (format.isValid())
-        d = new QAudioBufferPrivate(new QMemoryAudioBufferProvider(0, numSamples, format, startTime));
+        d = new QAudioBufferPrivate(new QMemoryAudioBufferProvider(0, numFrames, format, startTime));
     else
         d = 0;
 }
@@ -292,13 +292,13 @@ QAudioBuffer::~QAudioBuffer()
 
 /*!
     Returns true if this is a valid buffer.  A valid buffer
-    has more than zero samples in it and a valid format.
+    has more than zero frames in it and a valid format.
  */
 bool QAudioBuffer::isValid() const
 {
     if (!d || !d->mProvider)
         return false;
-    return d->mProvider->format().isValid() && (d->mProvider->sampleCount() > 0);
+    return d->mProvider->format().isValid() && (d->mProvider->frameCount() > 0);
 }
 
 /*!
@@ -306,7 +306,7 @@ bool QAudioBuffer::isValid() const
 
     Several properties of this format influence how
     the \l duration() or \l byteCount() are calculated
-    from the \l sampleCount().
+    from the \l frameCount().
  */
 QAudioFormat QAudioBuffer::format() const
 {
@@ -316,6 +316,19 @@ QAudioFormat QAudioBuffer::format() const
 }
 
 /*!
+    Returns the number of complete audio frames in this buffer.
+
+    An audio frame is an interleaved set of one sample per channel
+    for the same instant in time.
+*/
+int QAudioBuffer::frameCount() const
+{
+    if (!isValid())
+        return 0;
+    return d->mProvider->frameCount();
+}
+
+/*!
     Returns the number of samples in this buffer.
 
     If the format of this buffer has multiple channels,
@@ -323,12 +336,15 @@ QAudioFormat QAudioBuffer::format() const
     that a stereo buffer with 1000 samples in total will
     have 500 left samples and 500 right samples (interleaved),
     and this function will return 1000.
- */
+
+    \sa frameCount()
+*/
 int QAudioBuffer::sampleCount() const
 {
     if (!isValid())
         return 0;
-    return d->mProvider->sampleCount();
+
+    return frameCount() * format().channelCount();
 }
 
 /*!
@@ -337,21 +353,17 @@ int QAudioBuffer::sampleCount() const
 int QAudioBuffer::byteCount() const
 {
     const QAudioFormat f(format());
-    return (f.sampleSize() * sampleCount()) / 8; // sampleSize is in bits
+    return format().bytesForFrames(frameCount());
 }
 
 /*!
     Returns the duration of audio in this buffer, in microseconds.
 
-    This depends on the /l format(), and the \l sampleCount().
+    This depends on the /l format(), and the \l frameCount().
 */
 qint64 QAudioBuffer::duration() const
 {
-    int divisor = format().sampleRate() * format().channelCount();
-    if (divisor > 0)
-        return (sampleCount() * 1000000LL) / divisor;
-    else
-        return 0;
+    return format().durationForFrames(frameCount());
 }
 
 /*!
@@ -471,7 +483,7 @@ void *QAudioBuffer::data()
     }
 
     // Wasn't writable, so turn it into a memory provider
-    QAbstractAudioBuffer *memBuffer = new QMemoryAudioBufferProvider(constData(), sampleCount(), format(), startTime());
+    QAbstractAudioBuffer *memBuffer = new QMemoryAudioBufferProvider(constData(), frameCount(), format(), startTime());
 
     if (memBuffer) {
         d->mProvider->release();
@@ -487,35 +499,35 @@ void *QAudioBuffer::data()
 // Template helper classes worth documenting
 
 /*!
-    \class QAudioBuffer::StereoSampleDefault
+    \class QAudioBuffer::StereoFrameDefault
     \internal
 
     Just a trait class for the default value.
 */
 
 /*!
-    \class QAudioBuffer::StereoSample
-    \brief The StereoSample class provides a simple wrapper for a stereo audio sample.
+    \class QAudioBuffer::StereoFrame
+    \brief The StereoFrame class provides a simple wrapper for a stereo audio frame.
     \inmodule QtMultimedia
     \ingroup multimedia
     \ingroup multimedia_audio
 
     This templatized structure lets you treat a block of individual samples as an
-    interleaved stereo stream.  This is most useful when used with the templatized
+    interleaved stereo stream frame.  This is most useful when used with the templatized
     \l {QAudioBuffer::data()}{data()} functions of QAudioBuffer.  Generally the data
     is accessed as a pointer, so no copying should occur.
 
     There are some predefined instantiations of this template for working with common
     stereo sample depths in a convenient way.
 
-    This structure has \e left and \e right members for accessing individual channel data.
+    This frame structure has \e left and \e right members for accessing individual channel data.
 
     For example:
     \code
     // Assuming 'buffer' is an unsigned 16 bit stereo buffer..
-    QAudioBuffer::S16U *sample = buffer->data<QAudioBuffer::S16U>();
-    for (int i=0; i < buffer->sampleCount() / 2; i++) {
-        qSwap(sample[i].left, sample[i].right);
+    QAudioBuffer::S16U *frames = buffer->data<QAudioBuffer::S16U>();
+    for (int i=0; i < buffer->frameCount(); i++) {
+        qSwap(frames[i].left, frames[i].right);
     }
     \endcode
 
@@ -523,77 +535,77 @@ void *QAudioBuffer::data()
 */
 
 /*!
-    \fn QAudioBuffer::StereoSample::StereoSample()
+    \fn QAudioBuffer::StereoFrame::StereoFrame()
 
-    Constructs a new sample with the "silent" value for this
+    Constructs a new frame with the "silent" value for this
     sample format (0 for signed formats and floats, 0x8* for unsigned formats).
 */
 
 /*!
-    \fn QAudioBuffer::StereoSample::StereoSample(T leftSample, T rightSample)
+    \fn QAudioBuffer::StereoFrame::StereoFrame(T leftSample, T rightSample)
 
-    Constructs a new sample with the supplied \a leftSample and \a rightSample values.
+    Constructs a new frame with the supplied \a leftSample and \a rightSample values.
 */
 
 /*!
-    \fn QAudioBuffer::StereoSample::operator=(const StereoSample &other)
+    \fn QAudioBuffer::StereoFrame::operator=(const StereoFrame &other)
 
-    Assigns \a other to this sample.
+    Assigns \a other to this frame.
  */
 
 
 /*!
-    \fn QAudioBuffer::StereoSample::average() const
+    \fn QAudioBuffer::StereoFrame::average() const
 
     Returns the arithmetic average of the left and right samples.
  */
 
-/*! \fn QAudioBuffer::StereoSample::clear()
+/*! \fn QAudioBuffer::StereoFrame::clear()
 
-    Sets the values of this sample to the "silent" value.
+    Sets the values of this frame to the "silent" value.
 */
 
 /*!
-    \variable QAudioBuffer::StereoSample::left
+    \variable QAudioBuffer::StereoFrame::left
     \brief the left sample
 */
 
 /*!
-    \variable QAudioBuffer::StereoSample::right
+    \variable QAudioBuffer::StereoFrame::right
     \brief the right sample
 */
 
 /*!
     \typedef QAudioBuffer::S8U
-    \relates QAudioBuffer::StereoSample
+    \relates QAudioBuffer::StereoFrame
 
     This is a predefined specialization for an unsigned stereo 8 bit sample.  Each
     channel is an \e {unsigned char}.
 */
 /*!
     \typedef QAudioBuffer::S8S
-    \relates QAudioBuffer::StereoSample
+    \relates QAudioBuffer::StereoFrame
 
     This is a predefined specialization for a signed stereo 8 bit sample.  Each
     channel is a \e {signed char}.
 */
 /*!
     \typedef QAudioBuffer::S16U
-    \relates QAudioBuffer::StereoSample
+    \relates QAudioBuffer::StereoFrame
 
     This is a predefined specialization for an unsigned stereo 16 bit sample.  Each
     channel is an \e {unsigned short}.
 */
 /*!
     \typedef QAudioBuffer::S16S
-    \relates QAudioBuffer::StereoSample
+    \relates QAudioBuffer::StereoFrame
 
     This is a predefined specialization for a signed stereo 16 bit sample.  Each
     channel is a \e {signed short}.
 */
 /*!
     \typedef QAudioBuffer::S32F
-    \relates QAudioBuffer::StereoSample
+    \relates QAudioBuffer::StereoFrame
 
     This is a predefined specialization for an 32 bit float sample.  Each
     channel is a \e float.
diff --git a/src/multimedia/audio/qaudiobuffer.h b/src/multimedia/audio/qaudiobuffer.h
index 14718cb38..ac16e2182 100644
--- a/src/multimedia/audio/qaudiobuffer.h
+++ b/src/multimedia/audio/qaudiobuffer.h
@@ -65,7 +65,7 @@ public:
     QAudioBuffer(QAbstractAudioBuffer *provider);
     QAudioBuffer(const QAudioBuffer &other);
     QAudioBuffer(const QByteArray &data, const QAudioFormat &format, qint64 startTime = -1);
-    QAudioBuffer(int numSamples, const QAudioFormat &format, qint64 startTime = -1); // Initialized to empty
+    QAudioBuffer(int numFrames, const QAudioFormat &format, qint64 startTime = -1); // Initialized to empty
 
     QAudioBuffer& operator=(const QAudioBuffer &other);
 
@@ -75,6 +75,7 @@ public:
 
     QAudioFormat format() const;
 
+    int frameCount() const;
     int sampleCount() const;
     int byteCount() const;
 
@@ -93,23 +94,23 @@ public:
     void *data(); // detaches
 
     // Structures for easier access to stereo data
-    template <typename T> struct StereoSampleDefault { enum { Default = 0 }; };
+    template <typename T> struct StereoFrameDefault { enum { Default = 0 }; };
 
-    template <typename T> struct StereoSample {
+    template <typename T> struct StereoFrame {
 
-        StereoSample()
-            : left(T(StereoSampleDefault<T>::Default))
-            , right(T(StereoSampleDefault<T>::Default))
+        StereoFrame()
+            : left(T(StereoFrameDefault<T>::Default))
+            , right(T(StereoFrameDefault<T>::Default))
         {
         }
 
-        StereoSample(T leftSample, T rightSample)
+        StereoFrame(T leftSample, T rightSample)
             : left(leftSample)
             , right(rightSample)
         {
         }
 
-        StereoSample& operator=(const StereoSample &other)
+        StereoFrame& operator=(const StereoFrame &other)
         {
             // Two straight assigns is probably
             // cheaper than a conditional check on
@@ -123,14 +124,14 @@ public:
         T right;
 
         T average() const {return (left + right) / 2;}
-        void clear() {left = right = T(StereoSampleDefault<T>::Default);}
+        void clear() {left = right = T(StereoFrameDefault<T>::Default);}
     };
 
-    typedef StereoSample<unsigned char> S8U;
-    typedef StereoSample<signed char> S8S;
-    typedef StereoSample<unsigned short> S16U;
-    typedef StereoSample<signed short> S16S;
-    typedef StereoSample<float> S32F;
+    typedef StereoFrame<unsigned char> S8U;
+    typedef StereoFrame<signed char> S8S;
+    typedef StereoFrame<unsigned short> S16U;
+    typedef StereoFrame<signed short> S16S;
+    typedef StereoFrame<float> S32F;
 
     template <typename T> const T* constData() const {
         return static_cast<const T*>(constData());
@@ -145,8 +146,8 @@ private:
     QAudioBufferPrivate *d;
 };
 
-template <> struct QAudioBuffer::StereoSampleDefault<unsigned char> { enum { Default = 128 }; };
-template <> struct QAudioBuffer::StereoSampleDefault<unsigned short> { enum { Default = 32768 }; };
+template <> struct QAudioBuffer::StereoFrameDefault<unsigned char> { enum { Default = 128 }; };
+template <> struct QAudioBuffer::StereoFrameDefault<unsigned short> { enum { Default = 32768 }; };
 
 
 QT_END_NAMESPACE
diff --git a/src/multimedia/audio/qaudiobuffer_p.h b/src/multimedia/audio/qaudiobuffer_p.h
index 854ca23fc..5f6d3168a 100644
--- a/src/multimedia/audio/qaudiobuffer_p.h
+++ b/src/multimedia/audio/qaudiobuffer_p.h
@@ -66,7 +66,7 @@ public:
     // Format related
     virtual QAudioFormat format() const = 0;
     virtual qint64 startTime() const = 0;
-    virtual int sampleCount() const = 0;
+    virtual int frameCount() const = 0;
 
     // R/O Data
     virtual void *constData() const = 0;
diff --git a/src/multimedia/audio/qaudioformat.cpp b/src/multimedia/audio/qaudioformat.cpp
index c91620b37..32e17a9f9 100644
--- a/src/multimedia/audio/qaudioformat.cpp
+++ b/src/multimedia/audio/qaudioformat.cpp
@@ -146,7 +146,8 @@ public:
 
     This class is typically used in conjunction with QAudioInput or
     QAudioOutput to allow you to specify the parameters of the audio
-    stream being read or written.
+    stream being read or written, or with QAudioBuffer when dealing with
+    samples in memory.
 
     You can obtain audio formats compatible with the audio device used
     through functions in QAudioDeviceInfo. This class also lets you
@@ -154,6 +155,11 @@ public:
     the parameters yourself. See the \l QAudioDeviceInfo class
     description for details. You need to know the format of the audio
     streams you wish to play or record.
+
+    In the common case of interleaved linear PCM data, the codec will
+    be "audio/pcm", and the samples for all channels will be interleaved.
+    One sample for each channel for the same instant in time is referred
+    to as a frame in QtMultimedia (and other places).
 */
 
 /*!
@@ -282,6 +288,8 @@ void QAudioFormat::setSampleSize(int sampleSize)
 
 /*!
     Returns the current sample size value, in bits.
+
+    \sa bytesPerFrame()
 */
 int QAudioFormat::sampleSize() const
 {
@@ -345,6 +353,108 @@ QAudioFormat::SampleType QAudioFormat::sampleType() const
 }
 
 /*!
+    Returns the number of bytes required for this audio format for \a duration microseconds.
+
+    Returns 0 if this format is not valid.
+
+    Note that some rounding may occur if \a duration is not an exact fraction of the
+    sampleRate().
+
+    \sa durationForBytes()
+ */
+qint32 QAudioFormat::bytesForDuration(qint64 duration) const
+{
+    return bytesPerFrame() * framesForDuration(duration);
+}
+
+/*!
+    Returns the number of microseconds represented by \a bytes in this format.
+
+    Returns 0 if this format is not valid.
+
+    Note that some rounding may occur if \a bytes is not an exact multiple
+    of the number of bytes per frame.
+
+    \sa bytesForDuration()
+*/
+qint64 QAudioFormat::durationForBytes(qint32 bytes) const
+{
+    if (!isValid() || bytes <= 0)
+        return 0;
+
+    // We round the byte count to ensure whole frames
+    return qint64(1000000LL * (bytes / bytesPerFrame())) / sampleRate();
+}
+
+/*!
+    Returns the number of bytes required for \a frameCount frames of this format.
+
+    Returns 0 if this format is not valid.
+
+    \sa bytesForDuration()
+*/
+qint32 QAudioFormat::bytesForFrames(qint32 frameCount) const
+{
+    return frameCount * bytesPerFrame();
+}
+
+/*!
+    Returns the number of frames represented by \a byteCount in this format.
+
+    Note that some rounding may occur if \a byteCount is not an exact multiple
+    of the number of bytes per frame.
+
+    Each frame has one sample per channel.
+
+    \sa framesForDuration()
+*/
+qint32 QAudioFormat::framesForBytes(qint32 byteCount) const
+{
+    int size = bytesPerFrame();
+    if (size > 0)
+        return byteCount / size;
+    return 0;
+}
+
+/*!
+    Returns the number of frames required to represent \a duration microseconds in this format.
+
+    Note that some rounding may occur if \a duration is not an exact fraction of the
+    \l sampleRate().
+*/
+qint32 QAudioFormat::framesForDuration(qint64 duration) const
+{
+    if (!isValid())
+        return 0;
+
+    return qint32((duration * sampleRate()) / 1000000LL);
+}
+
+/*!
+    Return the number of microseconds represented by \a frameCount frames in this format.
+*/
+qint64 QAudioFormat::durationForFrames(qint32 frameCount) const
+{
+    if (!isValid() || frameCount <= 0)
+        return 0;
+
+    return (frameCount * 1000000LL) / sampleRate();
+}
+
+/*!
+    Returns the number of bytes required to represent one frame (a sample in each channel) in this format.
+
+    Returns 0 if this format is invalid.
+*/
+int QAudioFormat::bytesPerFrame() const
+{
+    if (!isValid())
+        return 0;
+
+    return (sampleSize() * channelCount()) / 8;
+}
+
+/*!
     \enum QAudioFormat::SampleType
 
     \value Unknown       Not Set
diff --git a/src/multimedia/audio/qaudioformat.h b/src/multimedia/audio/qaudioformat.h
index 3bc5780d6..fccb206eb 100644
--- a/src/multimedia/audio/qaudioformat.h
+++ b/src/multimedia/audio/qaudioformat.h
@@ -91,6 +91,18 @@ public:
     void setSampleType(QAudioFormat::SampleType sampleType);
     QAudioFormat::SampleType sampleType() const;
 
+    // Helper functions
+    qint32 bytesForDuration(qint64 duration) const;
+    qint64 durationForBytes(qint32 byteCount) const;
+
+    qint32 bytesForFrames(qint32 frameCount) const;
+    qint32 framesForBytes(qint32 byteCount) const;
+
+    qint32 framesForDuration(qint64 duration) const;
+    qint64 durationForFrames(qint32 frameCount) const;
+
+    int bytesPerFrame() const;
+
 private:
     QSharedDataPointer<QAudioFormatPrivate> d;
 };