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List:       kde-multimedia
Subject:    [PATCH] resampling fix for mpeglib
From:       Stefan Westerfeld <stefan () space ! twc ! de>
Date:       2000-08-23 20:52:28
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Hi!

Here is yet-another-patch for making mpeglib resample correct in those cases
where the samplingrate is something like 32000. The essential part here is
not the float -> double conversion but this section:

     // calculate how many input samples we need, then to satisfy the request
-    float wantWavSamples = ((float)samples+byteMultiplikator)*speed;
+    // use a larger amount than "really" required, to ensure that samples are
+    // available for rounding errors and interpolation
+    double wantWavSamples = (double)samples*speed+8.0;
 
Adding 8.0 should be a pretty safe choice for covering up both: float -> int
rounding errors here and in the actual conversion, and the fact that you need
more than one sample to do interpolation (currently one more due to linear
interpolation). The byteMultiplikator seems to have nothing to do with the
problem here, so I removed it.

Full patch is attached.

   Cu... Stefan
-- 
  -* Stefan Westerfeld, stefan@space.twc.de (PGP!), Hamburg/Germany
     KDE Developer, project infos at http://space.twc.de/~stefan/kde *-         

["mpeglib-resampling.diff" (text/plain)]

Index: decoderBaseObject_impl.cpp
===================================================================
RCS file: /home/kde/kdemultimedia/mpeglib_artsplug/decoderBaseObject_impl.cpp,v
retrieving revision 1.9
diff -u -r1.9 decoderBaseObject_impl.cpp
--- decoderBaseObject_impl.cpp	2000/08/17 12:01:52	1.9
+++ decoderBaseObject_impl.cpp	2000/08/23 20:38:17
@@ -286,10 +286,12 @@
     
     // calculate "how fast" we consume input samples (2.0 means, we need 2
     // input samples to generate one output sample)
-    float speed = (float)wav_samplingRate / samplingRateFloat;
+    double speed = (double)wav_samplingRate / (double)samplingRateFloat;
     
     // calculate how many input samples we need, then to satisfy the request
-    float wantWavSamples = ((float)samples+byteMultiplikator)*speed;
+    // use a larger amount than "really" required, to ensure that samples are
+    // available for rounding errors and interpolation
+    double wantWavSamples = (double)samples*speed+8.0;
 
     // convert that into bytes and try to read that many bytes
     wantBytes=(int) (wantWavSamples*byteMultiplikator);
@@ -308,7 +310,7 @@
     //haveSamples=samples;
     // calculate where we are now (as floating point position) in our
     // inputsample buffer
-    flpos += (float)haveSamples * speed;
+    flpos += (double)haveSamples * speed;
     
     // Good - so how many input samples we won't need anymore (for the
     // next request)? Skip them.
Index: decoderBaseObject_impl.h
===================================================================
RCS file: /home/kde/kdemultimedia/mpeglib_artsplug/decoderBaseObject_impl.h,v
retrieving revision 1.4
diff -u -r1.4 decoderBaseObject_impl.h
--- decoderBaseObject_impl.h	2000/07/18 19:23:47	1.4
+++ decoderBaseObject_impl.h	2000/08/23 20:38:18
@@ -49,7 +49,7 @@
   DecoderPlugin* decoderPlugin;
   InputStream* inputStream;
   ArtsOutputStream* outputStream;
-  float flpos;
+  double flpos;
   float startTime;
   int instance;
   int lastAudioBufferSize;

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