cannam@85: /*
cannam@85:  * libmad - MPEG audio decoder library
cannam@85:  * Copyright (C) 2000-2004 Underbit Technologies, Inc.
cannam@85:  *
cannam@85:  * This program is free software; you can redistribute it and/or modify
cannam@85:  * it under the terms of the GNU General Public License as published by
cannam@85:  * the Free Software Foundation; either version 2 of the License, or
cannam@85:  * (at your option) any later version.
cannam@85:  *
cannam@85:  * This program is distributed in the hope that it will be useful,
cannam@85:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
cannam@85:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
cannam@85:  * GNU General Public License for more details.
cannam@85:  *
cannam@85:  * You should have received a copy of the GNU General Public License
cannam@85:  * along with this program; if not, write to the Free Software
cannam@85:  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
cannam@85:  *
cannam@85:  * $Id: minimad.c,v 1.4 2004/01/23 09:41:32 rob Exp $
cannam@85:  */
cannam@85: 
cannam@85: # include <stdio.h>
cannam@85: # include <unistd.h>
cannam@85: # include <sys/stat.h>
cannam@85: # include <sys/mman.h>
cannam@85: 
cannam@85: # include "mad.h"
cannam@85: 
cannam@85: /*
cannam@85:  * This is perhaps the simplest example use of the MAD high-level API.
cannam@85:  * Standard input is mapped into memory via mmap(), then the high-level API
cannam@85:  * is invoked with three callbacks: input, output, and error. The output
cannam@85:  * callback converts MAD's high-resolution PCM samples to 16 bits, then
cannam@85:  * writes them to standard output in little-endian, stereo-interleaved
cannam@85:  * format.
cannam@85:  */
cannam@85: 
cannam@85: static int decode(unsigned char const *, unsigned long);
cannam@85: 
cannam@85: int main(int argc, char *argv[])
cannam@85: {
cannam@85:   struct stat stat;
cannam@85:   void *fdm;
cannam@85: 
cannam@85:   if (argc != 1)
cannam@85:     return 1;
cannam@85: 
cannam@85:   if (fstat(STDIN_FILENO, &stat) == -1 ||
cannam@85:       stat.st_size == 0)
cannam@85:     return 2;
cannam@85: 
cannam@85:   fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, STDIN_FILENO, 0);
cannam@85:   if (fdm == MAP_FAILED)
cannam@85:     return 3;
cannam@85: 
cannam@85:   decode(fdm, stat.st_size);
cannam@85: 
cannam@85:   if (munmap(fdm, stat.st_size) == -1)
cannam@85:     return 4;
cannam@85: 
cannam@85:   return 0;
cannam@85: }
cannam@85: 
cannam@85: /*
cannam@85:  * This is a private message structure. A generic pointer to this structure
cannam@85:  * is passed to each of the callback functions. Put here any data you need
cannam@85:  * to access from within the callbacks.
cannam@85:  */
cannam@85: 
cannam@85: struct buffer {
cannam@85:   unsigned char const *start;
cannam@85:   unsigned long length;
cannam@85: };
cannam@85: 
cannam@85: /*
cannam@85:  * This is the input callback. The purpose of this callback is to (re)fill
cannam@85:  * the stream buffer which is to be decoded. In this example, an entire file
cannam@85:  * has been mapped into memory, so we just call mad_stream_buffer() with the
cannam@85:  * address and length of the mapping. When this callback is called a second
cannam@85:  * time, we are finished decoding.
cannam@85:  */
cannam@85: 
cannam@85: static
cannam@85: enum mad_flow input(void *data,
cannam@85: 		    struct mad_stream *stream)
cannam@85: {
cannam@85:   struct buffer *buffer = data;
cannam@85: 
cannam@85:   if (!buffer->length)
cannam@85:     return MAD_FLOW_STOP;
cannam@85: 
cannam@85:   mad_stream_buffer(stream, buffer->start, buffer->length);
cannam@85: 
cannam@85:   buffer->length = 0;
cannam@85: 
cannam@85:   return MAD_FLOW_CONTINUE;
cannam@85: }
cannam@85: 
cannam@85: /*
cannam@85:  * The following utility routine performs simple rounding, clipping, and
cannam@85:  * scaling of MAD's high-resolution samples down to 16 bits. It does not
cannam@85:  * perform any dithering or noise shaping, which would be recommended to
cannam@85:  * obtain any exceptional audio quality. It is therefore not recommended to
cannam@85:  * use this routine if high-quality output is desired.
cannam@85:  */
cannam@85: 
cannam@85: static inline
cannam@85: signed int scale(mad_fixed_t sample)
cannam@85: {
cannam@85:   /* round */
cannam@85:   sample += (1L << (MAD_F_FRACBITS - 16));
cannam@85: 
cannam@85:   /* clip */
cannam@85:   if (sample >= MAD_F_ONE)
cannam@85:     sample = MAD_F_ONE - 1;
cannam@85:   else if (sample < -MAD_F_ONE)
cannam@85:     sample = -MAD_F_ONE;
cannam@85: 
cannam@85:   /* quantize */
cannam@85:   return sample >> (MAD_F_FRACBITS + 1 - 16);
cannam@85: }
cannam@85: 
cannam@85: /*
cannam@85:  * This is the output callback function. It is called after each frame of
cannam@85:  * MPEG audio data has been completely decoded. The purpose of this callback
cannam@85:  * is to output (or play) the decoded PCM audio.
cannam@85:  */
cannam@85: 
cannam@85: static
cannam@85: enum mad_flow output(void *data,
cannam@85: 		     struct mad_header const *header,
cannam@85: 		     struct mad_pcm *pcm)
cannam@85: {
cannam@85:   unsigned int nchannels, nsamples;
cannam@85:   mad_fixed_t const *left_ch, *right_ch;
cannam@85: 
cannam@85:   /* pcm->samplerate contains the sampling frequency */
cannam@85: 
cannam@85:   nchannels = pcm->channels;
cannam@85:   nsamples  = pcm->length;
cannam@85:   left_ch   = pcm->samples[0];
cannam@85:   right_ch  = pcm->samples[1];
cannam@85: 
cannam@85:   while (nsamples--) {
cannam@85:     signed int sample;
cannam@85: 
cannam@85:     /* output sample(s) in 16-bit signed little-endian PCM */
cannam@85: 
cannam@85:     sample = scale(*left_ch++);
cannam@85:     putchar((sample >> 0) & 0xff);
cannam@85:     putchar((sample >> 8) & 0xff);
cannam@85: 
cannam@85:     if (nchannels == 2) {
cannam@85:       sample = scale(*right_ch++);
cannam@85:       putchar((sample >> 0) & 0xff);
cannam@85:       putchar((sample >> 8) & 0xff);
cannam@85:     }
cannam@85:   }
cannam@85: 
cannam@85:   return MAD_FLOW_CONTINUE;
cannam@85: }
cannam@85: 
cannam@85: /*
cannam@85:  * This is the error callback function. It is called whenever a decoding
cannam@85:  * error occurs. The error is indicated by stream->error; the list of
cannam@85:  * possible MAD_ERROR_* errors can be found in the mad.h (or stream.h)
cannam@85:  * header file.
cannam@85:  */
cannam@85: 
cannam@85: static
cannam@85: enum mad_flow error(void *data,
cannam@85: 		    struct mad_stream *stream,
cannam@85: 		    struct mad_frame *frame)
cannam@85: {
cannam@85:   struct buffer *buffer = data;
cannam@85: 
cannam@85:   fprintf(stderr, "decoding error 0x%04x (%s) at byte offset %u\n",
cannam@85: 	  stream->error, mad_stream_errorstr(stream),
cannam@85: 	  stream->this_frame - buffer->start);
cannam@85: 
cannam@85:   /* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */
cannam@85: 
cannam@85:   return MAD_FLOW_CONTINUE;
cannam@85: }
cannam@85: 
cannam@85: /*
cannam@85:  * This is the function called by main() above to perform all the decoding.
cannam@85:  * It instantiates a decoder object and configures it with the input,
cannam@85:  * output, and error callback functions above. A single call to
cannam@85:  * mad_decoder_run() continues until a callback function returns
cannam@85:  * MAD_FLOW_STOP (to stop decoding) or MAD_FLOW_BREAK (to stop decoding and
cannam@85:  * signal an error).
cannam@85:  */
cannam@85: 
cannam@85: static
cannam@85: int decode(unsigned char const *start, unsigned long length)
cannam@85: {
cannam@85:   struct buffer buffer;
cannam@85:   struct mad_decoder decoder;
cannam@85:   int result;
cannam@85: 
cannam@85:   /* initialize our private message structure */
cannam@85: 
cannam@85:   buffer.start  = start;
cannam@85:   buffer.length = length;
cannam@85: 
cannam@85:   /* configure input, output, and error functions */
cannam@85: 
cannam@85:   mad_decoder_init(&decoder, &buffer,
cannam@85: 		   input, 0 /* header */, 0 /* filter */, output,
cannam@85: 		   error, 0 /* message */);
cannam@85: 
cannam@85:   /* start decoding */
cannam@85: 
cannam@85:   result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC);
cannam@85: 
cannam@85:   /* release the decoder */
cannam@85: 
cannam@85:   mad_decoder_finish(&decoder);
cannam@85: 
cannam@85:   return result;
cannam@85: }