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* libmad - MPEG audio decoder library
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* Copyright (C) 2000-2004 Underbit Technologies, Inc.
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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* $Id: minimad.c,v 1.4 2004/01/23 09:41:32 rob Exp $
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# include <sys/stat.h>
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# include <sys/mman.h>
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* This is perhaps the simplest example use of the MAD high-level API.
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* Standard input is mapped into memory via mmap(), then the high-level API
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* is invoked with three callbacks: input, output, and error. The output
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* callback converts MAD's high-resolution PCM samples to 16 bits, then
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* writes them to standard output in little-endian, stereo-interleaved
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static int decode(unsigned char const *, unsigned long);
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int main(int argc, char *argv[])
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if (fstat(STDIN_FILENO, &stat) == -1 ||
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fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, STDIN_FILENO, 0);
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if (fdm == MAP_FAILED)
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decode(fdm, stat.st_size);
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if (munmap(fdm, stat.st_size) == -1)
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* This is a private message structure. A generic pointer to this structure
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* is passed to each of the callback functions. Put here any data you need
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* to access from within the callbacks.
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unsigned char const *start;
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* This is the input callback. The purpose of this callback is to (re)fill
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* the stream buffer which is to be decoded. In this example, an entire file
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* has been mapped into memory, so we just call mad_stream_buffer() with the
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* address and length of the mapping. When this callback is called a second
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* time, we are finished decoding.
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enum mad_flow input(void *data,
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struct mad_stream *stream)
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struct buffer *buffer = data;
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mad_stream_buffer(stream, buffer->start, buffer->length);
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return MAD_FLOW_CONTINUE;
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* The following utility routine performs simple rounding, clipping, and
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* scaling of MAD's high-resolution samples down to 16 bits. It does not
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* perform any dithering or noise shaping, which would be recommended to
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* obtain any exceptional audio quality. It is therefore not recommended to
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* use this routine if high-quality output is desired.
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signed int scale(mad_fixed_t sample)
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sample += (1L << (MAD_F_FRACBITS - 16));
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if (sample >= MAD_F_ONE)
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sample = MAD_F_ONE - 1;
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else if (sample < -MAD_F_ONE)
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return sample >> (MAD_F_FRACBITS + 1 - 16);
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* This is the output callback function. It is called after each frame of
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* MPEG audio data has been completely decoded. The purpose of this callback
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* is to output (or play) the decoded PCM audio.
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enum mad_flow output(void *data,
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struct mad_header const *header,
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unsigned int nchannels, nsamples;
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mad_fixed_t const *left_ch, *right_ch;
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/* pcm->samplerate contains the sampling frequency */
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nchannels = pcm->channels;
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nsamples = pcm->length;
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left_ch = pcm->samples[0];
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right_ch = pcm->samples[1];
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/* output sample(s) in 16-bit signed little-endian PCM */
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sample = scale(*left_ch++);
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putchar((sample >> 0) & 0xff);
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putchar((sample >> 8) & 0xff);
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if (nchannels == 2) {
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sample = scale(*right_ch++);
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putchar((sample >> 0) & 0xff);
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putchar((sample >> 8) & 0xff);
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return MAD_FLOW_CONTINUE;
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* This is the error callback function. It is called whenever a decoding
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* error occurs. The error is indicated by stream->error; the list of
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* possible MAD_ERROR_* errors can be found in the mad.h (or stream.h)
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enum mad_flow error(void *data,
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struct mad_stream *stream,
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struct mad_frame *frame)
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struct buffer *buffer = data;
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fprintf(stderr, "decoding error 0x%04x (%s) at byte offset %u\n",
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stream->error, mad_stream_errorstr(stream),
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stream->this_frame - buffer->start);
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/* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */
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return MAD_FLOW_CONTINUE;
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* This is the function called by main() above to perform all the decoding.
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* It instantiates a decoder object and configures it with the input,
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* output, and error callback functions above. A single call to
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* mad_decoder_run() continues until a callback function returns
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* MAD_FLOW_STOP (to stop decoding) or MAD_FLOW_BREAK (to stop decoding and
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int decode(unsigned char const *start, unsigned long length)
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struct buffer buffer;
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struct mad_decoder decoder;
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/* initialize our private message structure */
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buffer.start = start;
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buffer.length = length;
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/* configure input, output, and error functions */
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mad_decoder_init(&decoder, &buffer,
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input, 0 /* header */, 0 /* filter */, output,
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error, 0 /* message */);
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result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC);
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/* release the decoder */
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mad_decoder_finish(&decoder);
added
removed
src/libmad/minimad.c
