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# minimad.c

    00001 /*
    00002  * libmad - MPEG audio decoder library
    00003  * Copyright (C) 2000-2003 Underbit Technologies, Inc.
    00004  *
    00005  * This program is free software; you can redistribute it and/or modify
    00006  * it under the terms of the GNU General Public License as published by
    00007  * the Free Software Foundation; either version 2 of the License, or
    00008  * (at your option) any later version.
    00009  *
    00010  * This program is distributed in the hope that it will be useful,
    00011  * but WITHOUT ANY WARRANTY; without even the implied warranty of
    00012  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    00013  * GNU General Public License for more details.
    00014  *
    00015  * You should have received a copy of the GNU General Public License
    00016  * along with this program; if not, write to the Free Software
    00017  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    00018  *
    00019  * $Id: minimad.c,v 1.1 2003/08/31 18:59:46 gabest Exp $
    00020  */
    00021
    00022 # include <stdio.h>
    00023 # include <unistd.h>
    00024 # include <sys/stat.h>
    00025 # include <sys/mman.h>
    00026
    00027 # include "mad.h"
    00028
    00029 /*
    00030  * This is perhaps the simplest example use of the MAD high-level API.
    00031  * Standard input is mapped into memory via mmap(), then the high-level API
    00032  * is invoked with three callbacks: input, output, and error. The output
    00033  * callback converts MAD's high-resolution PCM samples to 16 bits, then
    00034  * writes them to standard output in little-endian, stereo-interleaved
    00035  * format.
    00036  */
    00037
    00038 static int decode(unsigned char const *, unsigned long);
    00039
    00040 int main(int argc, char *argv[])
    00041 {
    00042   struct stat stat;
    00043   void *fdm;
    00044
    00045   if (argc != 1)
    00046     return 1;
    00047
    00048   if (fstat(STDIN_FILENO, &stat) == -1 ||
    00049       stat.st_size == 0)
    00050     return 2;
    00051
    00052   fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, STDIN_FILENO, 0);
    00053   if (fdm == MAP_FAILED)
    00054     return 3;
    00055
    00056   decode(fdm, stat.st_size);
    00057
    00058   if (munmap(fdm, stat.st_size) == -1)
    00059     return 4;
    00060
    00061   return 0;
    00062 }
    00063
    00064 /*
    00065  * This is a private message structure. A generic pointer to this structure
    00066  * is passed to each of the callback functions. Put here any data you need
    00067  * to access from within the callbacks.
    00068  */
    00069
    00070 struct buffer {
    00071   unsigned char const *start;
    00072   unsigned long length;
    00073 };
    00074
    00075 /*
    00076  * This is the input callback. The purpose of this callback is to (re)fill
    00077  * the stream buffer which is to be decoded. In this example, an entire file
    00078  * has been mapped into memory, so we just call mad_stream_buffer() with the
    00079  * address and length of the mapping. When this callback is called a second
    00080  * time, we are finished decoding.
    00081  */
    00082
    00083 static
    00084 enum mad_flow input(void *data,
    00085                     struct mad_stream *stream)
    00086 {
    00087   struct buffer *buffer = data;
    00088
    00089   if (!buffer->length)
    00090     return MAD_FLOW_STOP;
    00091
    00092   mad_stream_buffer(stream, buffer->start, buffer->length);
    00093
    00094   buffer->length = 0;
    00095
    00096   return MAD_FLOW_CONTINUE;
    00097 }
    00098
    00099 /*
    00100  * The following utility routine performs simple rounding, clipping, and
    00101  * scaling of MAD's high-resolution samples down to 16 bits. It does not
    00102  * perform any dithering or noise shaping, which would be recommended to
    00103  * obtain any exceptional audio quality. It is therefore not recommended to
    00104  * use this routine if high-quality output is desired.
    00105  */
    00106
    00107 static inline
    00108 signed int scale(mad_fixed_t sample)
    00109 {
    00110   /* round */
    00111   sample += (1L << (MAD_F_FRACBITS - 16));
    00112
    00113   /* clip */
    00114   if (sample >= MAD_F_ONE)
    00115     sample = MAD_F_ONE - 1;
    00116   else if (sample < -MAD_F_ONE)
    00117     sample = -MAD_F_ONE;
    00118
    00119   /* quantize */
    00120   return sample >> (MAD_F_FRACBITS + 1 - 16);
    00121 }
    00122
    00123 /*
    00124  * This is the output callback function. It is called after each frame of
    00125  * MPEG audio data has been completely decoded. The purpose of this callback
    00126  * is to output (or play) the decoded PCM audio.
    00127  */
    00128
    00129 static
    00130 enum mad_flow output(void *data,
    00131                      struct mad_header const *header,
    00132                      struct mad_pcm *pcm)
    00133 {
    00134   unsigned int nchannels, nsamples;
    00135   mad_fixed_t const *left_ch, *right_ch;
    00136
    00137   /* pcm->samplerate contains the sampling frequency */
    00138
    00139   nchannels = pcm->channels;
    00140   nsamples  = pcm->length;
    00141   left_ch   = pcm->samples[0];
    00142   right_ch  = pcm->samples[1];
    00143
    00144   while (nsamples--) {
    00145     signed int sample;
    00146
    00147     /* output sample(s) in 16-bit signed little-endian PCM */
    00148
    00149     sample = scale(*left_ch++);
    00150     putchar((sample >> 0) & 0xff);
    00151     putchar((sample >> 8) & 0xff);
    00152
    00153     if (nchannels == 2) {
    00154       sample = scale(*right_ch++);
    00155       putchar((sample >> 0) & 0xff);
    00156       putchar((sample >> 8) & 0xff);
    00157     }
    00158   }
    00159
    00160   return MAD_FLOW_CONTINUE;
    00161 }
    00162
    00163 /*
    00164  * This is the error callback function. It is called whenever a decoding
    00165  * error occurs. The error is indicated by stream->error; the list of
    00166  * possible MAD_ERROR_* errors can be found in the mad.h (or
    00167  * libmad/stream.h) header file.
    00168  */
    00169
    00170 static
    00171 enum mad_flow error(void *data,
    00172                     struct mad_stream *stream,
    00173                     struct mad_frame *frame)
    00174 {
    00175   struct buffer *buffer = data;
    00176
    00177   fprintf(stderr, "decoding error 0x%04x (%s) at byte offset %u\n",
    00178           stream->error, mad_stream_errorstr(stream),
    00179           stream->this_frame - buffer->start);
    00180
    00181   /* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */
    00182
    00183   return MAD_FLOW_CONTINUE;
    00184 }
    00185
    00186 /*
    00187  * This is the function called by main() above to perform all the
    00188  * decoding. It instantiates a decoder object and configures it with the
    00189  * input, output, and error callback functions above. A single call to
    00190  * mad_decoder_run() continues until a callback function returns
    00191  * MAD_FLOW_STOP (to stop decoding) or MAD_FLOW_BREAK (to stop decoding and
    00192  * signal an error).
    00193  */
    00194
    00195 static
    00196 int decode(unsigned char const *start, unsigned long length)
    00197 {
    00198   struct buffer buffer;
    00199   struct mad_decoder decoder;
    00200   int result;
    00201
    00202   /* initialize our private message structure */
    00203
    00204   buffer.start  = start;
    00205   buffer.length = length;
    00206
    00207   /* configure input, output, and error functions */
    00208
    00209   mad_decoder_init(&decoder, &buffer,
    00210                    input, 0 /* header */, 0 /* filter */, output,
    00211                    error, 0 /* message */);
    00212
    00213   /* start decoding */
    00214
    00215   result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC);
    00216
    00217   /* release the decoder */
    00218
    00219   mad_decoder_finish(&decoder);
    00220
    00221   return result;
    00222 }