include/wvrateadjust.h

   1 /* -*- Mode: C++ -*-
   2  * Worldvisions Weaver Software:
   3  *   Copyright (C) 1997-2002 Net Integration Technologies, Inc.
   4  *
   5  * WvRateAdjust is a WvEncoder that makes sure data comes out of it at a
   6  * given average rate.  It adds duplicate samples or removes extra samples
   7  * from the input in order to achieve this.
   8  *
   9  * The current version doesn't do anything fancy like linear or spline
  10  * interpolation, since it's being built mainly for minor rate adjustments
  11  * like 8000 Hz to 8020 Hz, and interpolation probably doesn't help too
  12  * much there.  It's also nicer to not have to worry explicitly about the
  13  * number format, which you would have to do if you were doing actual math.
  14  *
  15  * You can also use this as a slightly (not terribly) inefficient rate
  16  * *estimator* for the input stream.
  17  *
  18  * NOTE: Time is of the essence of this encoder.
  19  */
  20 #ifndef __WVRATEADJUST_H
  21 #define __WVRATEADJUST_H
  22
  23 #include "wvencoder.h"
  24 #include "wvtimeutils.h"
  25
  26 class WvRateAdjust : public WvEncoder
  27 {
  28 public:
  29     WvRateAdjust *match_rate;
  30
  31     int sampsize, irate_n, irate_d, orate_n, orate_d;
  32     WvTime epoch; // the time when sampling started
  33
  34     // the token bucket holds the "remainder" of our fake integer division
  35     // operation.  With this, we can make sure we always average out to
  36     // exactly the right rate.
  37     //
  38     // Basically:
  39     //    bucket = ((orate*insamps) - (irate*outsamps)) * irate_d * orate_d
  40     //
  41     // ...but with some care thrown in to prevent overflows.
  42     int bucket;
  43
  44     WvRateAdjust(int _sampsize, int _irate_base, int _orate);
  45     WvRateAdjust(int _sampsize, int _irate_base, WvRateAdjust *_match_rate);
  46
  47     int getirate()
  48         { return irate_n / irate_d; }
  49     int getorate()
  50         { return orate_n / orate_d; }
  51
  52 protected:
  53     void init(int _sampsize, int _irate_base);
  54
  55     virtual bool _encode(WvBuf &inbuf, WvBuf &outbuf, bool flush);
  56 };
  57
  58 #endif // __WVRATEADJUST_H