wavefile.c

   1 #include "wavefile.h"
   2 #include "stdint.h"
   3 #include "assert.h"
   4 #include "string.h"
   5 #include "attr.h"
   6 #include "errors.h"
   7
   8 struct wavehdr
   9 {
  10     // http://mathmatrix.narod.ru/Wavefmt.html
  11     char magic[4];      // "RIFF"
  12     uint32_t size;      // size of file
  13     char wave_magic[4]; // "WAVE"
  14     char fmt_magic[4];  // "fmt "
  15     uint32_t wave_section_chunk_size;
  16     uint16_t wave_fmt_type; // 1 = linear quantization
  17     uint16_t n_channels;
  18     uint32_t srate;
  19     uint32_t bytes_per_second;
  20     uint16_t block_align;
  21     uint16_t bits_per_sample;
  22 };
  23
  24 struct chunkhdr
  25 {
  26     char name[4];   // name of chunk
  27     uint32_t size;  // size (bytes) of chunk (excluding header)
  28 };
  29
  30 pure int waveformat_get_sample_size(const struct waveformat *restrict wf)
  31 {
  32     return (wf->bits / 8) * wf->channels;
  33 }
  34
  35 static err_t read_header(struct wavefile *wav)
  36 {
  37     struct wavehdr whdr;
  38     struct chunkhdr chdr;
  39
  40     // read wave header
  41     if (fread(&whdr, sizeof whdr, 1, wav->f) < 1){
  42         return make_error(EFREAD, wav, "%s: could not read wave file header", wav->filename);
  43     }
  44
  45     // check wave magic strings
  46     if (strncmp(whdr.magic, "RIFF", 4)
  47       || strncmp(whdr.wave_magic, "WAVE", 4)
  48       || strncmp(whdr.fmt_magic, "fmt ", 4)){
  49         // invalid file format
  50         return make_error(EFORMAT, wav, "%s: invalid wave file format", wav->filename);
  51     }
  52
  53     // make sure it's in PCM format
  54     if (whdr.wave_fmt_type != 1){
  55         return make_error(EFORMAT, wav, "%s: unsupported wave file format", wav->filename);
  56     }
  57
  58     // store format information
  59     wav->format.srate = whdr.srate;
  60     wav->format.bits = whdr.bits_per_sample;
  61     wav->format.channels = whdr.n_channels;
  62
  63     // read chunk headers
  64     for (;;){
  65         if (fread(&chdr, sizeof chdr, 1, wav->f) < 1){
  66             // read failure
  67             return 1;
  68         }
  69         if (!strncmp(chdr.name, "data", 4)){
  70             // found the data chunk
  71             break;
  72         } else {
  73             // this is not the data.
  74             // Next chunk!
  75             fseek(wav->f, chdr.size, SEEK_CUR);
  76         }
  77     }
  78
  79     wav->length = chdr.size / ((wav->format.bits / 8) * wav->format.channels);
  80     wav->pcm_start = ftell(wav->f);
  81     return 0;
  82 }
  83
  84 err_t wavefile_open(struct wavefile *wav, const char *filename)
  85 {
  86     // open the wave file
  87     wav->filename = filename; // TODO: dup?
  88     wav->f = fopen(filename, "r");
  89     if (!wav->f){
  90         return make_error(EFOPEN, wav, "%s: cannot open file", filename);
  91     }
  92
  93     // read wave file header
  94     return read_header(wav);
  95 }
  96
  97 err_t wavefile_read_at(struct wavefile *wav, off_t sample_start, void *buf, size_t n_samples)
  98 {
  99     if (sample_start + n_samples > wav->length){
 100         // past the end of file
 101         return make_error(EWAVE_EOF, wav, "%s: tried reading beyond the end of the file (at sample number %llu)", (unsigned long long) sample_start);
 102     }
 103
 104     fseek(wav->f, wav->pcm_start + sample_start * waveformat_get_sample_size(&wav->format), SEEK_SET);
 105     fread(buf, 1, n_samples * waveformat_get_sample_size(&wav->format), wav->f);
 106     return EOK;
 107 }