vorbis-tools/oggenc/resample.h

   1 /* This program is licensed under the GNU Library General Public License,
   2  * version 2, a copy of which is included with this program (LICENCE.LGPL).
   3  *
   4  * (c) 2002 Simon Hosie <gumboot@clear.net.nz>
   5  *
   6  *
   7  * A resampler
   8  *
   9  * reference:
  10  *     'Digital Filters', third edition, by R. W. Hamming  ISBN 0-486-65088-X
  11  *
  12  * history:
  13  *    2002-05-31    ready for the world (or some small section thereof)
  14  *
  15  *
  16  * TOOD:
  17  *     zero-crossing clipping in coefficient table
  18  */
  19
  20 #ifndef _RESAMPLE_H_INCLUDED
  21 #define _RESAMPLE_H_INCLUDED
  22
  23 typedef float SAMPLE;
  24
  25 typedef struct
  26 {
  27     unsigned int channels, infreq, outfreq, taps;
  28     float *table;
  29     SAMPLE *pool;
  30
  31     /* dynamic bits */
  32     int poolfill;
  33     int offset;
  34 } res_state;
  35
  36 typedef enum
  37 {
  38     RES_END,
  39     RES_GAIN,    /* (double)1.0 */
  40     RES_CUTOFF,    /* (double)0.80 */
  41     RES_TAPS,    /* (int)45 */
  42     RES_BETA    /* (double)16.0 */
  43 } res_parameter;
  44
  45 int res_init(res_state *state, int channels, int outfreq, int infreq, res_parameter op1, ...);
  46 /*
  47  * Configure *state to manage a data stream with the specified parameters.  The
  48  * string 'params' is currently unspecified, but will configure the parameters
  49  * of the filter.
  50  *
  51  * This function allocates memory, and requires that res_clear() be called when
  52  * the buffer is no longer needed.
  53  *
  54  *
  55  * All counts/lengths used in the following functions consider only the data in
  56  * a single channel, and in numbers of samples rather than bytes, even though
  57  * functionality will be mirrored across as many channels as specified here.
  58  */
  59
  60
  61 int res_push_max_input(res_state const *state, size_t maxoutput);
  62 /*
  63  *  Returns the maximum number of input elements that may be provided without
  64  *  risk of flooding an output buffer of size maxoutput.  maxoutput is
  65  *  specified in counts of elements, NOT in bytes.
  66  */
  67
  68
  69 int res_push_check(res_state const *state, size_t srclen);
  70 /*
  71  * Returns the number of elements that will be returned if the given srclen
  72  * is used in the next call to res_push().
  73  */
  74
  75
  76 int res_push(res_state *state, SAMPLE **dstlist, SAMPLE const **srclist, size_t srclen);
  77 int res_push_interleaved(res_state *state, SAMPLE *dest, SAMPLE const *source, size_t srclen);
  78 /*
  79  * Pushes srclen samples into the front end of the filter, and returns the
  80  * number of resulting samples.
  81  *
  82  * res_push(): srclist and dstlist point to lists of pointers, each of which
  83  * indicates the beginning of a list of samples.
  84  *
  85  * res_push_interleaved(): source and dest point to the beginning of a list of
  86  * interleaved samples.
  87  */
  88
  89
  90 int res_drain(res_state *state, SAMPLE **dstlist);
  91 int res_drain_interleaved(res_state *state, SAMPLE *dest);
  92 /*
  93  * Recover the remaining elements by flushing the internal pool with 0 values,
  94  * and storing the resulting samples.
  95  *
  96  * After either of these functions are called, *state should only re-used in a
  97  * final call to res_clear().
  98  */
  99
 100
 101 void res_clear(res_state *state);
 102 /*
 103  * Free allocated buffers, etc.
 104  */
 105
 106 #endif
 107