wav-file-info.js

// Hi Welcome to WFI by David Jones / RackFX, LLC
var fs = require('fs');
var wfi = {}

wfi.infoByFilename = function(filename, cb){
  var stats = fs.statSync(filename)
  var buffer = new Buffer(40);  // first 40 bytes are RIFF header
  fs.open(filename, 'r', function(err, fd) {
    if(err) return cb(err);  // error probably TODO:check this!

    // ex error -
    // { [Error: ENOENT: no such file or directory, open './test.wav'] errno: -2, code: 'ENOENT', syscall: 'open', path: './test.wav' }
    var read_result = {}


    // this a list of sequenced bytes in the 40 byte header. This builds the read_result object.
    //  Property name / Data type / Length
    var reads = [
      ['riff_head', 'string', 4],
      ['chunk_size','uinteger', 4],
      ['wave_identifier', 'string', 4],
      ['fmt_identifier', 'string', 4],
      ['subchunk_size','integer',4],
      ['audio_format','integer',2],
      ['num_channels','integer',2],
      ['sample_rate','uinteger',4],
      ['byte_rate','integer',4],
      ['block_align','integer',2],
      ['bits_per_sample','integer',2],
      //['uhm','integer',2],
      ['data_identifier','string', 4],
      //['sub_chunk2_size', 'integer', 4],

    ]
    fs.read(fd, buffer, 0, 40, 0, function(err, num) {

      var i=0;
      var pointer = 0;
      function read_wav(){
        var read = reads[i];

        i++;
        if(read[1]=='string'){
          read_result[read[0]] = buffer.toString('ascii', pointer , pointer + read[2]);
          pointer = pointer + read[2];   // pointer = pointer plus # bytes
        }
        else if(read[1]=='integer'){

          read_result[read[0]] = buffer.readUInt16LE(pointer, read[2])
          pointer = pointer + read[2];
        }
        else if(read[1]=='uinteger'){

          read_result[read[0]] = buffer.readInt32LE(pointer, read[2])
          pointer = pointer + read[2];
        }
        if(i < reads.length) { return read_wav()}
        else { return fs.close(fd, post_process); }

      }
      //console.log(i)
      read_wav();
    }); // end fs.read

    function post_process(){
      var error = false;
      var invalid_reasons = []

      if (read_result.riff_head != "RIFF")  invalid_reasons.push("Expected \"RIFF\" string at 0" )
      if (read_result.wave_identifier != "WAVE") invalid_reasons.push("Expected \"WAVE\" string at 4")
      if (read_result.fmt_identifier != "fmt ") invalid_reasons.push("Expected \"fmt \" string at 8")
      if (
        (read_result.audio_format != 1) &&        // Wav PCM
        (read_result.audio_format != 65534)  &&   // Extensible PCM
        (read_result.audio_format != 2)  &&       // Wav
        (read_result.audio_format != 6) &&        // Wav ALAW
        (read_result.audio_format != 7) &&        // Wav MULAW
        (read_result.audio_format != 22127)  &&   // Vorbis ?? (issue #11)
        (read_result.audio_format != 3))          // Wav
              invalid_reasons.push("Unknown format: "+read_result.audio_format)
      if ((read_result.chunk_size + 8) !== stats.size) invalid_reasons.push("chunk_size does not match file size")
      //if ((read_result.data_identifier) != "data") invalid_reasons.push("Expected data identifier at the end of the header")

      if (invalid_reasons.length > 0) error = true;

      if (error) return cb({
        error : true,
        invalid_reasons: invalid_reasons,
        header: read_result,
        stats: stats
      });

      cb(null, {
        header: read_result,
        stats: stats,
        duration: ((read_result.chunk_size) / (read_result.sample_rate * read_result.num_channels * (read_result.bits_per_sample / 8)))
      });
    }
  });
}
module.exports = wfi;