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/* * libmad - MPEG audio decoder library * Copyright (C) 2000-2003 Underbit Technologies, Inc. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * $Id: minimad.c,v 1.2 2003/06/05 02:27:07 rob Exp $ */ # include <stdio.h> # include <unistd.h> # include <sys/stat.h> # include <sys/mman.h> # include "mad.h" /* * This is perhaps the simplest example use of the MAD high-level API. * Standard input is mapped into memory via mmap(), then the high-level API * is invoked with three callbacks: input, output, and error. The output * callback converts MAD's high-resolution PCM samples to 16 bits, then * writes them to standard output in little-endian, stereo-interleaved * format. */ static int fd_dsp; /* * This is a private message structure. A generic pointer to this structure * is passed to each of the callback functions. Put here any data you need * to access from within the callbacks. */ struct buffer { unsigned char const *start; unsigned long length; }; /* * This is the input callback. The purpose of this callback is to (re)fill * the stream buffer which is to be decoded. In this example, an entire file * has been mapped into memory, so we just call mad_stream_buffer() with the * address and length of the mapping. When this callback is called a second * time, we are finished decoding. */ static enum mad_flow input(void *data, struct mad_stream *stream) { struct buffer *buffer = data; if (!buffer->length) return MAD_FLOW_STOP; mad_stream_buffer(stream, buffer->start, buffer->length); buffer->length = 0; return MAD_FLOW_CONTINUE; } /* * The following utility routine performs simple rounding, clipping, and * scaling of MAD's high-resolution samples down to 16 bits. It does not * perform any dithering or noise shaping, which would be recommended to * obtain any exceptional audio quality. It is therefore not recommended to * use this routine if high-quality output is desired. */ static inline signed int scale(mad_fixed_t sample) { /* round */ sample += (1L << (MAD_F_FRACBITS - 16)); /* clip */ if (sample >= MAD_F_ONE) sample = MAD_F_ONE - 1; else if (sample < -MAD_F_ONE) sample = -MAD_F_ONE; /* quantize */ return sample >> (MAD_F_FRACBITS + 1 - 16); } /* * This is the output callback function. It is called after each frame of * MPEG audio data has been completely decoded. The purpose of this callback * is to output (or play) the decoded PCM audio. */ static enum mad_flow output(void *data, struct mad_header const *header, struct mad_pcm *pcm) { unsigned int nchannels, nsamples; mad_fixed_t const *left_ch, *right_ch; /* pcm->samplerate contains the sampling frequency */ nchannels = pcm->channels; nsamples = pcm->length; left_ch = pcm->samples[0]; right_ch = pcm->samples[1]; #if 0 while (nsamples--) { signed int sample; /* output sample(s) in 16-bit signed little-endian PCM */ sample = scale(*left_ch++); putchar((sample >> 0) & 0xff); putchar((sample >> 8) & 0xff); if (nchannels == 2) { sample = scale(*right_ch++); putchar((sample >> 0) & 0xff); putchar((sample >> 8) & 0xff); } } #else while (nsamples--) { signed int sample; short buf; /* output sample(s) in 16-bit signed little-endian PCM */ sample = scale(*left_ch++); buf = sample & 0xFFFF; write(fd_dsp, &buf, 2); if (nchannels == 2) { sample = scale(*right_ch++); buf = sample & 0xFFFF; write(fd_dsp, &buf, 2); } } #endif return MAD_FLOW_CONTINUE; } /* * This is the error callback function. It is called whenever a decoding * error occurs. The error is indicated by stream->error; the list of * possible MAD_ERROR_* errors can be found in the mad.h (or * libmad/stream.h) header file. */ static enum mad_flow error(void *data, struct mad_stream *stream, struct mad_frame *frame) { struct buffer *buffer = data; fprintf(stderr, "decoding error 0x%04x (%s) at byte offset %u\n", stream->error, mad_stream_errorstr(stream), stream->this_frame - buffer->start); /* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */ return MAD_FLOW_CONTINUE; } /* * This is the function called by main() above to perform all the * decoding. It instantiates a decoder object and configures it with the * input, output, and error callback functions above. A single call to * mad_decoder_run() continues until a callback function returns * MAD_FLOW_STOP (to stop decoding) or MAD_FLOW_BREAK (to stop decoding and * signal an error). */ int decode(unsigned char const *start, unsigned long length, int fd) { struct buffer buffer; struct mad_decoder decoder; int result; /* sound device */ fd_dsp = fd; /* initialize our private message structure */ buffer.start = start; buffer.length = length; /* configure input, output, and error functions */ mad_decoder_init(&decoder, &buffer, input, 0 /* header */, 0 /* filter */, output, error, 0 /* message */); /* start decoding */ result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC); /* release the decoder */ mad_decoder_finish(&decoder); return result; }