/**
002 * libmad - MPEG audio decoder library
003 * Copyright (C) 2000-2004 Underbit Technologies, Inc.
004 *
005 * This program is free software; you can redistribute it and/or modify
006 * it under the terms of the GNU General Public License as published by
007 * the Free Software Foundation; either version 2 of the License, or
008 * (at your option) any later version.
009 *
010 * This program is distributed in the hope that it will be useful,
011 * but WITHOUT ANY WARRANTY; without even the implied warranty of
012 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
013 * GNU General Public License for more details.
014 *
015 * You should have received a copy of the GNU General Public License
016 * along with this program; if not, write to the Free Software
017 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
018 *
019 * $Id: minimad.c,v 1.4 2004/01/23 09:41:32 rob Exp $
020 */
021
022 # include <stdio.h>
023 # include <unistd.h>
024 # include <sys/stat.h>
025 # include <sys/mman.h>
026
027 # include "mad.h"
028
029 /**
030 * This is perhaps the simplest example use of the MAD high-level API.
031 * Standard input is mapped into memory via mmap(), then the high-level API
032 * is invoked with three callbacks: input, output, and error. The output
033 * callback converts MAD's high-resolution PCM samples to 16 bits, then
034 * writes them to standard output in little-endian, stereo-interleaved
035 * format.
036 */
037
038 static int decode(unsigned char const *, unsigned long);
039
040 int main(int argc, char *argv[])
041 {
042 struct stat stat;
043 void *fdm;
044
045 if (argc != 1)
046 return 1;
047
048 if (fstat(STDIN_FILENO, &stat) == -1 ||
049 stat.st_size == 0)
050 return 2;
051
052 fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, STDIN_FILENO, 0);
053 if (fdm == MAP_FAILED)
054 return 3;
055
056 decode(fdm, stat.st_size);
057
058 if (munmap(fdm, stat.st_size) == -1)
059 return 4;
060
061 return 0;
062 }
063
064 /**
065 * This is a private message structure. A generic pointer to this structure
066 * is passed to each of the callback functions. Put here any data you need
067 * to access from within the callbacks.
068 */
069
070 struct buffer {
071 unsigned char const *start;
072 unsigned long length;
073 };
074
075 /**
076 * This is the input callback. The purpose of this callback is to (re)fill
077 * the stream buffer which is to be decoded. In this example, an entire file
078 * has been mapped into memory, so we just call mad_stream_buffer() with the
079 * address and length of the mapping. When this callback is called a second
080 * time, we are finished decoding.
081 */
082
083 static
084 enum mad_flow input(void *data,
085 struct mad_stream *stream)
086 {
087 struct buffer *buffer = data;
088
089 if (!buffer->length)
090 return MAD_FLOW_STOP;
091
092 mad_stream_buffer(stream, buffer->start, buffer->length);
093
094 buffer->length = 0;
095
096 return MAD_FLOW_CONTINUE;
097 }
098
099 /**
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 }
