add AudioFrame.duration() for convenience

src/AudioFrame.cpp

@@ -1,6 +1,6 @@
 /******************************************************************************
     QtAV:  Media play library based on Qt and FFmpeg
-    Copyright (C) 2012-2015 Wang Bin <[email protected]>
+    Copyright (C) 2012-2016 Wang Bin <[email protected]>
 
 *   This file is part of QtAV
 
@@ -189,6 +189,12 @@ void AudioFrame::setAudioResampler(AudioResampler *conv)
     d_func()->conv = conv;
 }
 
+qint64 AudioFrame::duration() const
+{
+    Q_D(const AudioFrame);
+    return d->format.durationForBytes(d->data.size());
+}
+
 AudioFrame AudioFrame::to(const AudioFormat &fmt) const
 {
     if (!isValid() || !constBits(0))

src/QtAV/AudioFrame.h

@@ -1,6 +1,6 @@
 /******************************************************************************
     QtAV:  Media play library based on Qt and FFmpeg
-    Copyright (C) 2012-2015 Wang Bin <[email protected]>
+    Copyright (C) 2012-2016 Wang Bin <[email protected]>
 
 *   This file is part of QtAV
 
@@ -70,6 +70,13 @@ class Q_AV_EXPORT AudioFrame : public Frame
     AudioFrame to(const AudioFormat& fmt) const;
     //AudioResamplerId
     void setAudioResampler(AudioResampler *conv); //TODO: remove
+    /*!
+        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.
+    */
+    qint64 duration() const;
 };
 
 } //namespace QtAV