apps/codecs/libmad/minimad.c

   1 /*
   2  * libmad - MPEG audio decoder library
   3  * Copyright (C) 2000-2004 Underbit Technologies, Inc.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18  *
  19  * $Id$
  20  */
  21
  22 # include <stdio.h>
  23 # include <unistd.h>
  24 # include <sys/stat.h>
  25 # include <sys/mman.h>
  26
  27 # include "mad.h"
  28
  29 /*
  30  * This is perhaps the simplest example use of the MAD high-level API.
  31  * Standard input is mapped into memory via mmap(), then the high-level API
  32  * is invoked with three callbacks: input, output, and error. The output
  33  * callback converts MAD's high-resolution PCM samples to 16 bits, then
  34  * writes them to standard output in little-endian, stereo-interleaved
  35  * format.
  36  */
  37
  38 static int decode(unsigned char const *, unsigned long);
  39
  40 int main(int argc, char *argv[])
  41 {
  42   struct stat stat;
  43   void *fdm;
  44
  45   if (argc != 1)
  46     return 1;
  47
  48   if (fstat(STDIN_FILENO, &stat) == -1 ||
  49       stat.st_size == 0)
  50     return 2;
  51
  52   fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, STDIN_FILENO, 0);
  53   if (fdm == MAP_FAILED)
  54     return 3;
  55
  56   decode(fdm, stat.st_size);
  57
  58   if (munmap(fdm, stat.st_size) == -1)
  59     return 4;
  60
  61   return 0;
  62 }
  63
  64 /*
  65  * This is a private message structure. A generic pointer to this structure
  66  * is passed to each of the callback functions. Put here any data you need
  67  * to access from within the callbacks.
  68  */
  69
  70 struct buffer {
  71   unsigned char const *start;
  72   unsigned long length;
  73 };
  74
  75 /*
  76  * This is the input callback. The purpose of this callback is to (re)fill
  77  * the stream buffer which is to be decoded. In this example, an entire file
  78  * has been mapped into memory, so we just call mad_stream_buffer() with the
  79  * address and length of the mapping. When this callback is called a second
  80  * time, we are finished decoding.
  81  */
  82
  83 static
  84 enum mad_flow input(void *data,
  85                     struct mad_stream *stream)
  86 {
  87   struct buffer *buffer = data;
  88
  89   if (!buffer->length)
  90     return MAD_FLOW_STOP;
  91
  92   mad_stream_buffer(stream, buffer->start, buffer->length);
  93
  94   buffer->length = 0;
  95
  96   return MAD_FLOW_CONTINUE;
  97 }
  98
  99 /*
 100  * The following utility routine performs simple rounding, clipping, and
 101  * scaling of MAD's high-resolution samples down to 16 bits. It does not
 102  * perform any dithering or noise shaping, which would be recommended to
 103  * obtain any exceptional audio quality. It is therefore not recommended to
 104  * use this routine if high-quality output is desired.
 105  */
 106
 107 static inline
 108 signed int scale(mad_fixed_t sample)
 109 {
 110   /* round */
 111   sample += (1L << (MAD_F_FRACBITS - 16));
 112
 113   /* clip */
 114   if (sample >= MAD_F_ONE)
 115     sample = MAD_F_ONE - 1;
 116   else if (sample < -MAD_F_ONE)
 117     sample = -MAD_F_ONE;
 118
 119   /* quantize */
 120   return sample >> (MAD_F_FRACBITS + 1 - 16);
 121 }
 122
 123 /*
 124  * This is the output callback function. It is called after each frame of
 125  * MPEG audio data has been completely decoded. The purpose of this callback
 126  * is to output (or play) the decoded PCM audio.
 127  */
 128
 129 static
 130 enum mad_flow output(void *data,
 131                      struct mad_header const *header,
 132                      struct mad_pcm *pcm)
 133 {
 134   unsigned int nchannels, nsamples;
 135   mad_fixed_t const *left_ch, *right_ch;
 136
 137   /* pcm->samplerate contains the sampling frequency */
 138
 139   nchannels = pcm->channels;
 140   nsamples  = pcm->length;
 141   left_ch   = pcm->samples[0];
 142   right_ch  = pcm->samples[1];
 143
 144   while (nsamples--) {
 145     signed int sample;
 146
 147     /* output sample(s) in 16-bit signed little-endian PCM */
 148
 149     sample = scale(*left_ch++);
 150     putchar((sample >> 0) & 0xff);
 151     putchar((sample >> 8) & 0xff);
 152
 153     if (nchannels == 2) {
 154       sample = scale(*right_ch++);
 155       putchar((sample >> 0) & 0xff);
 156       putchar((sample >> 8) & 0xff);
 157     }
 158   }
 159
 160   return MAD_FLOW_CONTINUE;
 161 }
 162
 163 /*
 164  * This is the error callback function. It is called whenever a decoding
 165  * error occurs. The error is indicated by stream->error; the list of
 166  * possible MAD_ERROR_* errors can be found in the mad.h (or stream.h)
 167  * header file.
 168  */
 169
 170 static
 171 enum mad_flow error(void *data,
 172                     struct mad_stream *stream,
 173                     struct mad_frame *frame)
 174 {
 175   struct buffer *buffer = data;
 176
 177   fprintf(stderr, "decoding error 0x%04x (%s) at byte offset %u\n",
 178           stream->error, mad_stream_errorstr(stream),
 179           stream->this_frame - buffer->start);
 180
 181   /* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */
 182
 183   return MAD_FLOW_CONTINUE;
 184 }
 185
 186 /*
 187  * This is the function called by main() above to perform all the decoding.
 188  * It instantiates a decoder object and configures it with the input,
 189  * output, and error callback functions above. A single call to
 190  * mad_decoder_run() continues until a callback function returns
 191  * MAD_FLOW_STOP (to stop decoding) or MAD_FLOW_BREAK (to stop decoding and
 192  * signal an error).
 193  */
 194
 195 static
 196 int decode(unsigned char const *start, unsigned long length)
 197 {
 198   struct buffer buffer;
 199   struct mad_decoder decoder;
 200   int result;
 201
 202   /* initialize our private message structure */
 203
 204   buffer.start  = start;
 205   buffer.length = length;
 206
 207   /* configure input, output, and error functions */
 208
 209   mad_decoder_init(&decoder, &buffer,
 210                    input, 0 /* header */, 0 /* filter */, output,
 211                    error, 0 /* message */);
 212
 213   /* start decoding */
 214
 215   result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC);
 216
 217   /* release the decoder */
 218
 219   mad_decoder_finish(&decoder);
 220
 221   return result;
 222 }