Wav merge

gistfile1.m

// a bit hackish way of merging two wav files, assumes raw samples.

#import <Foundation/Foundation.h>

#define RIFF_ID 0x52494646 // "RIFF"
#define RIFF_FMT_ID 0x666d7420 // "fmt "
#define RIFF_DATA_ID 0x64617461 // "data"

typedef struct riffChunkHeader {
  UInt32 rsc_id; // big endian
  UInt32 rsc_size; // little endian
} riffChunkHeader_t;

NSData *extractRiffChunk(NSData *riffData, UInt32 extractId, BOOL extractOnlyData);
NSData *extractRiffChunkAll(NSData *riffData, UInt32 extractId);
NSData *extractRiffChunkData(NSData *riffData, UInt32 extractId);

NSData *extractRiffChunk(NSData *riffData, UInt32 extractId, BOOL extractOnlyData) {
  NSUInteger offset = 0;
  
  while (([riffData length] - offset) >= sizeof(riffChunkHeader_t)) {
    NSData *riffChunkRange = [riffData subdataWithRange:
                              NSMakeRange(offset, sizeof(riffChunkHeader_t))];
    const riffChunkHeader_t *riffChunk = [riffChunkRange bytes];
    UInt32 riffId = NSSwapBigIntToHost(riffChunk->rsc_id);
    NSUInteger riffSize = NSSwapLittleIntToHost(riffChunk->rsc_size);
    // treat RIFF chunk as a subchunk containing format
    if (riffId == RIFF_ID) {
      riffSize = 4;
    }
    
    if (riffId != extractId) {
      offset += sizeof(riffChunkHeader_t) + riffSize;
      continue;
    }
    
    NSUInteger len;
    if (extractOnlyData) {
      offset += sizeof(riffChunkHeader_t);
      len = riffSize;
    } else {
      len = sizeof(riffChunkHeader_t) + riffSize;
    }
    
    if (([riffData length] - offset) < riffSize) {
      break;
    }
    
    return [riffData subdataWithRange:NSMakeRange(offset, len)];
  }
  
  return nil;
}

NSData *extractRiffChunkAll(NSData *riffData, UInt32 extractId) {
  return extractRiffChunk(riffData, extractId, NO);
}

NSData *extractRiffChunkData(NSData *riffData, UInt32 extractId) {
  return extractRiffChunk(riffData, extractId, YES);
}

NSData *mergeWavFiles(NSData *wavData1, NSData *wavData2);

NSData *mergeWavFiles(NSData *wavData1, NSData *wavData2) {
  NSMutableData *riffAll = [[extractRiffChunkAll(wavData1, RIFF_ID)
                             mutableCopy]
                            autorelease];
  NSData *fmtAll = extractRiffChunkAll(wavData1, RIFF_FMT_ID);
  NSData *file1Data = extractRiffChunkData(wavData1, RIFF_DATA_ID);
  NSData *file2Data = extractRiffChunkData(wavData2, RIFF_DATA_ID);
  
  riffChunkHeader_t riffDataSubChunk;
  riffDataSubChunk.rsc_id = NSSwapHostIntToBig(RIFF_DATA_ID);
  riffDataSubChunk.rsc_size = NSSwapHostIntToLittle((UInt32)[file1Data length] +
                                                    (UInt32)[file2Data length]);
  NSData *dataHeader = [NSData dataWithBytes:&riffDataSubChunk
                                      length:sizeof(riffDataSubChunk)];
  
  riffChunkHeader_t *riffChunk = [riffAll mutableBytes];
  riffChunk->rsc_size = NSSwapHostIntToLittle(sizeof(riffChunkHeader_t) +
                                              (UInt32)[fmtAll length] +
                                              (UInt32)[dataHeader length] +
                                              (UInt32)[file1Data length] +
                                              (UInt32)[file2Data length]);
  
  NSMutableData *mergedWav = [NSMutableData data];
  [mergedWav appendData:riffAll];
  [mergedWav appendData:fmtAll];
  [mergedWav appendData:dataHeader];
  [mergedWav appendData:file1Data];
  [mergedWav appendData:file2Data];
  
  return mergedWav;
}

int main (int argc, const char * argv[])
{
  @autoreleasepool {
    [mergeWavFiles([NSData dataWithContentsOfURL:
                    [NSURL URLWithString:@"file:///path/to/test1.wav"]],
                   [NSData dataWithContentsOfURL:
                    [NSURL URLWithString:@"file:///path/to/test2.wav"]])
     writeToURL:[NSURL URLWithString:@"file:///path/to/merged.wav"]
     atomically:YES];
  }
  return 0;
}