🚀 go-pugleaf

This code snippet should extract the length of a Wav file.
It has been ripped out of some other code I had here, so I hope it compiles
without any problems.

Fredrik Kvamme



#include <stdio.h>

class RIFFChunk {
public:
   int ID;              // 4 char ID. "RIFF", "WAVE", "fmt ", "DATA"
   int ChunkSize;
};


class RIFFHeader : public RIFFChunk {
public:
   int Format;         // 'WAVE'
};

class RIFFWAVEFormat : public RIFFChunk {
public:
   short int AudioFmt;
   short int NumChannels;
   int SampleRate;
   int ByteRate;
   short int BlockAlign;
   short int BitsPerSample;
};



float GetWAVLength(AnsiString FileName)
{
  FILE *infile;
  RIFFHeader riffHeader; // All RIFF files start with this header
  RIFFWAVEFormat riffFormat; // Then follows the Wave format

  RIFFChunk riffData; // The last part is the wave samples. We only need the
                                  // size of this part so we read only the
RIFFChunk.

  int BitsPerSample;
  int NumChannels;
  int SampleRate;
  int NumSamples;

  infile=fopen(FileName.c_str(),"rb");
  fread(&riffHeader,sizeof(riffHeader),1,infile);
  // Check that the file header makes sense.
  if (riffHeader.ID!=*(int*)"RIFF" ) {
    throw Exception((AnsiString)"Expected RIFF header.");
  }
  // Check that the format is Wave
  if (riffHeader.Format!=*(int*)"WAVE" ) {
    throw Exception((AnsiString)"Expected RIFF format to be WAVE.");
  }
  // Read the format chunk
  fread(&riffFormat,sizeof(riffFormat),1,infile);
  // Check that we have got the format header.
  if (riffFormat.ID!=*(int*)"fmt ") {
    throw Exception((AnsiString)"Expected the format chunk to be the first
chunk.");
  }
  // Check that we have got a PCM file. No idea how to calculate size for a
compressed file...
  if (riffFormat.AudioFmt!=1) {
    throw Exception((AnsiString)"Unexpected Wave format. Expected PCM. Got:
" + riffFormat.AudioFmt);
  }
  // Copy the format data to the internal structures.
  BitsPerSample=riffFormat.BitsPerSample;
  NumChannels=riffFormat.NumChannels;
  SampleRate=riffFormat.SampleRate;
  // Move the filepointer if the chunksize is different from the riffFormat
structure we are using.
  // This might be the case if the format chunk is extended.
  fseek(infile,8+riffFormat.ChunkSize-sizeof(riffFormat),SEEK_CUR);

  // Next struct is the Wave data chunk. We don't need the samples, only the
size so we will only read the RIFFChunk part.
  // Read the datachunk in one operation:-) We love multimegabyte reads!
  fread(&riffData,sizeof(riffData),1,infile);
  fclose(infile); //  We are done with the file now.
  // Lots of different encodings but it is only the 8 bit format which is
coded as 1 byte per sample.
  int BytesPerSample=((BitsPerSample==8)?1:2);
  // Now we can get the number of samples from the chunksizefield in the
datachunk.
  NumSamples=riffData.ChunkSize/(NumChannels*BytesPerSample);
  // We return the number of seconds.
  return NumSamples/SampleRate;
}