wav_io.c

Motion JPEG编解码器源代码

/*
    wav_io: Utilities for dealing with WAV files

    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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include "mjpeg_logging.h"
#include "wav_io.h"


/*
   wav_read_header: Read and analyze the header of a WAV file.

   The file must be positioned at start before the call

   The file is positioned at the start of the audio data after the call.

   This program is written so that it can be used on big and little endian
   machines and that it can be used on a pipe (no seeks)


   returns 0 on success, -1 on error
*/

static int hdr_len = 0;

static uint32_t getulong(uint8_t *data)
{
   /* Interprets data as a little endian number */

   return (data[0] | (data[1]<<8) | (data[2]<<16) | (data[3]<<24));
}

static int32_t find_tag(FILE *fd, const char *tag)
{
   uint8_t data[8];
   uint32_t m;
   int n;

   /* scan input stream for specified tag and return its length */
   /* returns -1 in case of error */

   while(1)
   {
      n = fread(data,1,8,fd);
      if(n!=8) goto error;

      hdr_len += 8;

      m = getulong(data+4);
      if(!strncasecmp((char*)data,tag,4)) return m;

      for(n=0;n<m;n++)
         if(fgetc(fd)==EOF) goto error;

      hdr_len += m;
   }

error:
   mjpeg_error("EOF in WAV header when searching for tag \"%s\"",tag);
   return -1;
}

int wav_read_header(FILE *fd, int *rate, int *chans, int *bits,
                    int *format, int32_t *bytes)
{
   int32_t fmt_len;
   uint32_t riff_len, m;
   uint8_t data[16];
   int n;

   n = fread(data,1,12,fd);
   if(n!=12) {
	   mjpeg_error("EOF in WAV header");
      return -1;
   }

   if(strncasecmp((char*)data,"RIFF",4)) {
      mjpeg_error("Input not a WAV file - starts not with \"RIFF\"");
      return -1;
   }

   riff_len = getulong(data+4);

   if(strncasecmp((char*)data+8,"WAVE",4)) {
      mjpeg_error("Input not a WAV file - has no \"WAVE\" tag");
      return -1;
   }

   hdr_len = 12;

   fmt_len = find_tag(fd,"fmt ");
   if(fmt_len<0) return -1;
   if(fmt_len&1) fmt_len++;
   if(fmt_len<16) {
      mjpeg_error("WAV format len %d too short",fmt_len);
      return -1;
   }

   n = fread(data,1,16,fd);
   if(n!=16) {
      mjpeg_error("EOF in WAV header");
      return -1;
   }

   m = getulong(data);        /* wFormatTag + nChannels */
   *format = m&0xffff;
   *chans  = (m>>16) & 0xffff;

   *rate = getulong(data+4);  /* nSamplesPerSec */

   m = getulong(data+8);      /* nAvgBytesPerSec */

   m = getulong(data+12);     /* nBlockAlign + wBitsPerSample */
   *bits = (m>>16) & 0xffff;

   /* skip over remaining bytes in format (if any) */

   for(n=16;n<fmt_len;n++) fgetc(fd);

   hdr_len += fmt_len;

   /* Get data len */

   *bytes = find_tag(fd,"data");
   if(*bytes<0) return -1;

   if(*bytes+hdr_len != riff_len+8) {
      mjpeg_warn("File length according data tag: %u",*bytes+hdr_len);
      mjpeg_warn("File length according RIFF tag: %u",riff_len+8);
	  mjpeg_warn("Inconsistency is inevitable if wav's are being piped");
   }

   return 0;
}