我正在尝试操作波形文件头。我已将文件加载到 NSMutableData 中,并尝试更改 wav 文件头信息。我的问题就在于:
[maindata replaceBytesInRange:range withBytes:((UInt32 *)tfSC1Length)];
我收到 EXC_BAD_ACCESS 错误。不明白为什么。有什么想法吗?
我使用的代码如下:
// calculate total file length (minus 8 for the header), chunk size, number of channels, sample rate and bits per sample
int tfLength = ([maindata length] - 8);
int tfChannels = 1; // mono
int tfSampleRate = 44100;
int tfDataLength = ([maindata length] - 44);
int tfBitsPerSample = 16;
int tfSC1Length = 16;
int tfAudioFormat = 1;
//we are rebuilding the header for the wave files...
// chunk identifier
((char *)[maindata mutableBytes])[0] = 'R';
((char *)[maindata mutableBytes])[1] = 'I';
((char *)[maindata mutableBytes])[2] = 'F';
((char *)[maindata mutableBytes])[3] = 'F';
// size (less 8 bytes)
NSRange range;
range.location = 4;
range.length = 4;
[maindata replaceBytesInRange:range withBytes:(UInt32 *)tfLength];
// the file format
((char *)[maindata mutableBytes])[8] = 'W';
((char *)[maindata mutableBytes])[9] = 'A';
((char *)[maindata mutableBytes])[10] = 'V';
((char *)[maindata mutableBytes])[11] = 'E';
// subchunk1 ID
((char *)[maindata mutableBytes])[12] = 'f';
((char *)[maindata mutableBytes])[13] = 'm';
((char *)[maindata mutableBytes])[14] = 't';
((char *)[maindata mutableBytes])[15] = ' ';
// subchunk length
range.location = 16;
range.length = 4;
[maindata replaceBytesInRange:range withBytes:((UInt32 *)tfSC1Length)];
// audio format
range.location = 20;
range.length = 2;
[maindata replaceBytesInRange:range withBytes:((UInt16 *)tfAudioFormat)];
// number of channels
range.location = 22;
range.length = 2;
[maindata replaceBytesInRange:range withBytes:((UInt16 *)tfChannels)];
// sample rate
range.location = 24;
range.length = 4;
[maindata replaceBytesInRange:range withBytes:((UInt32 *)tfSampleRate)];
// byte rate
range.location = 28;
range.length = 4;
[maindata replaceBytesInRange:range withBytes:((UInt32 *)(tfSampleRate * ((tfBitsPerSample * tfChannels) / 8)))];
// block align
range.location = 32;
range.length = 2;
[maindata replaceBytesInRange:range withBytes:((UInt16 *)((tfBitsPerSample * tfChannels) / 8))];
// bits per sample
range.location = 34;
range.length = 2;
[maindata replaceBytesInRange:range withBytes:((UInt16 *)tfBitsPerSample)];
// adjust the length field of the wave file...
((char *)[maindata mutableBytes])[36] = 'd';
((char *)[maindata mutableBytes])[37] = 'a';
((char *)[maindata mutableBytes])[38] = 't';
((char *)[maindata mutableBytes])[39] = 'a';
// length of the audio data
range.location = 40;
range.length = 4;
[maindata replaceBytesInRange:range withBytes:(UInt32 *)tfDataLength];
最佳答案
我建议使用结构体来引用 header :
typedef struct {
UInt32 riffChunkID; // Always RIFF, in big endian. Integer fields are little-ending.
UInt32 fileLength;
UInt32 waveFileID; // 'WAVE' for Wave files.
UInt32 formatChunkID; // 'fmt '
UInt32 formatChunkSize;
SInt16 formatTag; // Wave Format ID: see constants
SInt16 channels; // Number of Channels: 1=mono, 2=stereo
SInt32 sampleRate; // Sample Rate: samples per second
SInt32 bytesPerSec; // sampleRate * blockAlign
SInt16 blockAlign; // sample frame size = channels * sampleSize / 8
SInt16 bitsPerSample; // sampleSize (8 or 16), also two's-complement for 16-bit, offset for 8-bit
UInt32 dataChunkID; // 'data'
UInt32 dataChunkSize;
} WaveHeader;
int tfChannels = 1; // mono
int tfSampleRate = 44100;
int tfBitsPerSample = 16;
WaveHeader *header = [maindata mutableBytes];
header->riffChunkID = CFSwapInt32HostToBig ('RIFF');
header->fileLength = CFSwapInt32HostToLittle ([maindata length] - 8);
header->waveFileID = CFSwapInt32HostToBig ('WAVE');
header->formatChunkID = CFSwapInt32HostToBig ('fmt ');
header->formatChunkSize = CFSwapInt32HostToLittle (16);
header->formatTag = CFSwapInt16HostToLittle (1);
header->channels = CFSwapInt16HostToLittle (tfChannels);
header->sampleRate = CFSwapInt32HostToLittle (tfSampleRate);
header->bytesPerSec = CFSwapInt32HostToLittle (tfSampleRate * tfBitsPerSample / 8 * tfChannels);
header->blockAlign = CFSwapInt16HostToLittle (tfBitsPerSample / 8 * tfChannels);
header->bitsPerSample = CFSwapInt16HostToLittle (tfBitsPerSample);
header->dataChunkID = CFSwapInt32HostToBig ('data');
header->dataChunkSize = CFSwapInt32HostToLittle ([maindata length] - 44);
短得多。希望这会有所帮助。
关于iphone - 操作 NSMutableData 中的字节问题 - Wave header 信息,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1992551/