wavefile.c

   1 #include "wavefile.h"
   2 #include "stdint.h"
   3 #include "assert.h"
   4 #include "string.h"
   5
   6 struct wavehdr
   7 {
   8     // http://mathmatrix.narod.ru/Wavefmt.html
   9     char magic[4];      // "RIFF"
  10     uint32_t size;      // size of file
  11     char wave_magic[4]; // "WAVE"
  12     char fmt_magic[4];  // "fmt "
  13     uint32_t wave_section_chunk_size;
  14     uint16_t wave_fmt_type; // 1 = linear quantization
  15     uint16_t n_channels;
  16     uint32_t srate;
  17     uint32_t bytes_per_second;
  18     uint16_t block_align;
  19     uint16_t bits_per_sample;
  20 };
  21
  22 struct chunkhdr
  23 {
  24     char name[4];   // name of chunk
  25     uint32_t size;  // size (bytes) of chunk (excluding header)
  26 };
  27
  28 static int read_header(struct wavefile *wav)
  29 {
  30     struct wavehdr whdr;
  31     struct chunkhdr chdr;
  32
  33     // read wave header
  34     if (fread(&whdr, sizeof whdr, 1, wav->f) < 1){
  35         return 1;
  36     }
  37
  38     // check wave magic strings
  39     if (strncmp(whdr.magic, "RIFF", 4)
  40       || strncmp(whdr.wave_magic, "WAVE", 4)
  41       || strncmp(whdr.fmt_magic, "fmt ", 4)){
  42         // invalid file format
  43         return 1;
  44     }
  45
  46     // make sure it's in PCM format
  47     if (whdr.wave_fmt_type != 1){
  48         return 1;
  49     }
  50
  51     // store format information
  52     wav->format.srate = whdr.srate;
  53     wav->format.bits = whdr.bits_per_sample;
  54     wav->format.channels = whdr.n_channels;
  55
  56     // read chunk headers
  57     for (;;){
  58         if (fread(&chdr, sizeof chdr, 1, wav->f) < 1){
  59             // read failure
  60             return 1;
  61         }
  62         if (!strncmp(chdr.name, "data", 4)){
  63             // found the data chunk
  64             break;
  65         } else {
  66             // this is not the data.
  67             // Next chunk!
  68             fseek(wav->f, chdr.size, SEEK_CUR);
  69         }
  70     }
  71
  72     wav->length = chdr.size / ((wav->format.bits / 8) * wav->format.channels);
  73     wav->pcm_start = ftell(wav->f);
  74     return 0;
  75 }
  76
  77 int wavefile_open(struct wavefile *wav, const char *filename)
  78 {
  79     // open the wave file
  80     wav->f = fopen(filename, "r");
  81     if (!wav->f){
  82         return 1;
  83     }
  84
  85     // read wave file header
  86     return read_header(wav);
  87 }
  88
  89 int wavefile_read_at(struct wavefile *wav, off_t sample_start, void *buf, size_t n_samples)
  90 {
  91     if (sample_start + n_samples > wav->length){
  92         // past the end of file
  93         return 1;
  94     }
  95
  96     fseek(wav->f, wav->pcm_start + sample_start * aformat_get_sample_size(&wav->format), SEEK_SET);
  97     fread(buf, 1, n_samples * aformat_get_sample_size(&wav->format), wav->f);
  98     return 0;
  99 }