Add mid function to AudioFrame to get an arbitrary portion of the frame

stormysky · Oct 13, 2017 · dff0967 · dff0967
1 parent 7bf1cbb
commit dff0967
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Showing 2 changed files with 36 additions and 8 deletions.
diff --git a/src/AudioFrame.cpp b/src/AudioFrame.cpp
@@ -132,23 +132,50 @@ int AudioFrame::channelCount() const
 }
 
 AudioFrame AudioFrame::clone() const
+{
+    return mid(0, -1);
+}
+
+AudioFrame AudioFrame::mid(int pos, int len) const
 {
     Q_D(const AudioFrame);
+
     if (d->format.sampleFormatFFmpeg() == AV_SAMPLE_FMT_NONE
-            || d->format.channels() <= 0)
+            || d->format.channels() <= 0) {
         return AudioFrame();
-    if (d->samples_per_ch <= 0 || bytesPerLine(0) <= 0)
+    }
+
+    if (d->samples_per_ch <= 0 || bytesPerLine(0) <= 0 || len == 0) {
         return AudioFrame(format());
-    QByteArray buf(bytesPerLine()*planeCount(), 0);
+    }
+
+    int bufSize = bytesPerLine();
+    int posBytes = 0;
+    if (pos > 0) {
+        posBytes = pos * d->format.bytesPerSample();
+        bufSize -= posBytes;
+    } else {
+        pos = 0;
+    }
+
+    int lenBytes = len * d->format.bytesPerSample();
+    if (len > 0 && lenBytes < bufSize) {
+        bufSize = lenBytes;
+    } else {
+        lenBytes = bufSize;
+    }
+
+    QByteArray buf(bufSize * planeCount(), 0);
     char *dst = buf.data(); //must before buf is shared, otherwise data will be detached.
+
     for (int i = 0; i < planeCount(); ++i) {
-        const int plane_size = bytesPerLine(i);
-        memcpy(dst, constBits(i), plane_size);
-        dst += plane_size;
+        memcpy(dst, constBits(i) + posBytes, lenBytes);
+        dst += lenBytes;
     }
+
     AudioFrame f(d->format, buf);
-    f.setSamplesPerChannel(samplesPerChannel());
-    f.setTimestamp(timestamp());
+    f.setSamplesPerChannel(bufSize / d->format.bytesPerSample());
+    f.setTimestamp(d->timestamp + (qreal) d->format.durationForBytes(posBytes) / AudioFormat::kHz);
     // meta data?
     return f;
 }

diff --git a/src/QtAV/AudioFrame.h b/src/QtAV/AudioFrame.h
@@ -57,6 +57,7 @@ class Q_AV_EXPORT AudioFrame : public Frame
      * then you can use clone().
      */
     AudioFrame clone() const;
+    AudioFrame mid(int pos, int len = -1) const;
     AudioFormat format() const;
     void setSamplesPerChannel(int samples);
     // may change after resampling