mp32pcm.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <mad.h>

#define ALOGE(...) printf(__VA_ARGS__);printf("\n")



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);
	//TODO save to pcm

    if (nchannels == 2) {
      sample = scale(*right_ch++);
      //putchar((sample >> 0) & 0xff);
      //putchar((sample >> 8) & 0xff);
		//TODO save to pcm
    }
  }

  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;
}

static 
enum mad_flow header(void* data, struct mad_header const * hdr){
	ALOGE("layer: %d", hdr->layer);
	ALOGE("mode: %d", hdr->mode);
	ALOGE("extension: %d", hdr->mode_extension);
	ALOGE("emphasis: %d", hdr->emphasis);
	ALOGE("bitrate: %d", hdr->bitrate);
	ALOGE("samplerate: %d", hdr->samplerate);
	ALOGE("crc_check: %d", hdr->crc_check);
	ALOGE("crc_target: %d", hdr->crc_target);
	ALOGE("flags: %d", hdr->flags);
	ALOGE("private_bits: %d", hdr->private_bits);
	ALOGE("duration: %ld.%u", hdr->duration.seconds, hdr->duration.fraction);
  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, header /* 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;
}

int main(int argc, char** argv)
{
	if (argc != 2){
		printf("usage: %s file.mp3\n", argv[0]);
		return 0;
	}
	int fd = open(argv[1], O_RDONLY);
	if (!fd) {
		ALOGE("fopen: %s", strerror(errno));
		//perror(path);
		//exit(EXIT_FAILURE);
		return 0;
	}
	struct stat sb;
	if (stat(argv[1], &sb)) {
		ALOGE("stat: %s", strerror(errno));
		//perror(path);
		// exit(EXIT_FAILURE);
		close(fd);
		return 0;
	}
	void* file_buf = mmap(0, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
	if(!file_buf || file_buf == MAP_FAILED){
		ALOGE("mmap: %s", strerror(errno));
		close(fd);
		return 0;
	}

	int rc = decode(file_buf, sb.st_size);
	if (rc){
		ALOGE("decode");
	}

	if(munmap(file_buf, sb.st_size) != 0){
		ALOGE("munmap: %s", strerror(errno));
	}
	close(fd);
	return 0;
}