comparison src/libmad-0.15.1b/minimad.c @ 85:545efbb81310

Import initial set of sources

+/*
+ * libmad - MPEG audio decoder library
+ * Copyright (C) 2000-2004 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 1.4 2004/01/23 09:41:32 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 decode(unsigned char const *, unsigned long);
+
+int main(int argc, char *argv[])
+{
+  struct stat stat;
+  void *fdm;
+
+  if (argc != 1)
+    return 1;
+
+  if (fstat(STDIN_FILENO, &stat) == -1 ||
+      stat.st_size == 0)
+    return 2;
+
+  fdm = mmap(0, stat.st_size, PROT_READ, MAP_SHARED, STDIN_FILENO, 0);
+  if (fdm == MAP_FAILED)
+    return 3;
+
+  decode(fdm, stat.st_size);
+
+  if (munmap(fdm, stat.st_size) == -1)
+    return 4;
+
+  return 0;
+}
+
+/*
+ * 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];
+
+  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);
+    }
+  }
+
+  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 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).
+ */
+
+static
+int decode(unsigned char const *start, unsigned long length)
+{
+  struct buffer buffer;
+  struct mad_decoder decoder;
+  int result;
+
+  /* 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;
+}