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实例分析：实现一个PHPWAV接合方案
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发布于：2011-01-26 22:05
 | |  |  | WAV PCM文件的最大好处在于，你无需进行所有绑定操作，就能将来自两个文件的二进制音频数据连接起来。你只需把其中一个文件的二进制数据粘合到另一个文件的末尾，再调整一下Subchunk2Size值，即可实现两个文件的接合。唯一的缺点是这两个文件的格式必须相同；在本例中，不涉及问题。
当解析音频文件时，先将二进制音频数据读入一个缓冲数组中，然后再将另一个文件的数据读到这个数组的末端。重复这一过程直到所有的文件都被读取完毕。创建一个FILESTRUCT结构，填入格式信息，调整Subchunk2Size值，将Data成员设为缓冲数组，将FILESTRUCT写为需要的输出格式。对于基于PHP的web发布系统，其输出为标准输出。以下为示范代码：
function StitchFiles(;$fsFile, ;$sFiles) {
$fsFiles = array(); //FILESTRUCT
$lFileSize = 0;
$lOffset = 0;
$bData = array(); //byte
for ($i = 0; $i < count($sFiles); $i++) {
$fsFiles[$i] = new FILESTRUCT();
SetFile($fsFiles[$i], $sFiles[$i]);
$lSize = CalcLittleEndianValue($fsFiles[$i]->Subchunk2Size);
$lFileSize = $lFileSize + $lSize;
$bData = array_merge($bData, $fsFiles[$i]->Data);
$lOffset = $lOffset + $lSize;
}
$fsFile->ChunkID = $GLOBALS["ChunkID_"];
$fsFile->ChunkSize = GetLittleEndianByteArray(36 + $lFileSize);
$fsFile->Format = $GLOBALS["FileFormat_"];
$fsFile->Subchunk1ID = $GLOBALS["Subchunk1ID_"];
$fsFile->Subchunk1Size = array(0x10, 0x0, 0x0, 0x0);
$fsFile->AudioFormat = $GLOBALS["AudioFormat_"];
$fsFile->NumChannels = $GLOBALS["Stereo_"];
$fsFile->SampleRate = $GLOBALS["SampleRate_"];
$fsFile->ByteRate = GetLittleEndianByteArray(
CalcLittleEndianValue($GLOBALS["SampleRate_"]) *
CalcLittleEndianValue($GLOBALS["Stereo_"]) *
(CalcLittleEndianValue($GLOBALS["BitsPerSample_"]) / 8));
$fsFile->BlockAlign =
array_splice(GetLittleEndianByteArray(CalcLittleEndianValue($GLOBALS["Stereo_"]
) * (CalcLittleEndianValue($GLOBALS["BitsPerSample_"]) / 8)), 0, 2);
$fsFile->BitsPerSample = $GLOBALS["BitsPerSample_"];
$fsFile->Subchunk2ID = $GLOBALS["Subchunk2ID_"];
$fsFile->Subchunk2Size = GetLittleEndianByteArray($lFileSize);
$fsFile->Data = $bData;
}
本调用的第一个参数是对FILESTRUCT对象的引用。第二个参数是对一列文件名字符串的引用。在每次for循环中，我都将列表中的一个文件名载入一个FILESTRUCT中，然后再将每一个FILESTRUCT的Data属性提取出来，并合并到一个现有的缓冲区中。完成以上操作后，我通过一个事先声明的全局变量对FILESTRUCT参数对象的属性进行设定，然后改动Subchunk2Size属性，并将Data属性设为新的缓冲区。
你可能注意到，我使用了一些功能函数来填充FILESTRUCT结构、计算来自little endian字节数组的数值、创建little endian字节数组和拆分字符串为二进制数组。以下为这些函数：
function SetFile(;$fsFile_, $sFileName) {
$lSize = 1;
if (file_exists($sFileName)) {
$fil = fopen($sFileName, "rb");
$contents = fread($fil, count($fsFile_->ChunkID));
$fsFile_->ChunkID = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->ChunkSize));
$fsFile_->ChunkSize = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->Format));
$fsFile_->Format = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->Subchunk1ID));
$fsFile_->Subchunk1ID = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->Subchunk1Size));
$fsFile_->Subchunk1Size = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->AudioFormat));
$fsFile_->AudioFormat = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->NumChannels));
$fsFile_->NumChannels = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->SampleRate));
$fsFile_->SampleRate = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->ByteRate));
$fsFile_->ByteRate = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->BlockAlign));
$fsFile_->BlockAlign = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->BitsPerSample));
$fsFile_->BitsPerSample = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->Subchunk2ID));
$fsFile_->Subchunk2ID = bin_split($contents, 1);
$contents = fread($fil, count($fsFile_->Subchunk2Size));
$fsFile_->Subchunk2Size = bin_split($contents, 1);
$lSize = CalcLittleEndianValue($fsFile_->Subchunk2Size);
$contents = fread($fil, $lSize);
$fsFile_->Data = bin_split($contents, 1);
fclose($fil);
}
}
function CalcLittleEndianValue(;$bValue) {
$lSize_ = 0;
for ($iByte = 0; $iByte < count($bValue); $iByte++) {
$lSize_ += ($bValue[$iByte] * pow(16, ($iByte * 2)));
}
return $lSize_;
}
function GetLittleEndianByteArray($lValue) {
$running = 0;
$b = array(0, 0, 0, 0);
$running = $lValue / pow(16,6);
$b[3] = floor($running);
$running -= $b[3];
$running *= 256;
$b[2] = floor($running);
$running -= $b[2];
$running *= 256;
$b[1] = floor($running);
$running -= $b[1];
$running *= 256;
$b[0] = round($running);
return $b;
}
function bin_split($text, $c)
{
$arr = array();
$len = strlen($text);
$a = 0;
while($a < $len)
{
if ($a + $c > $len)
{
$c = $len - $a;
}
$arr[$a] = ord(substr($text, $a, $c));
$a += $c;
}
return $arr;
}
为了实现这个类的功能，你能创建一个CStitcher实例并调用StitchFiles()方法，以传递合适的参数：
$ChunkID_ = array(0x52, 0x49, 0x46, 0x46); //"RIFF" big endian
$FileFormat_ = array(0x57, 0x41, 0x56, 0x45); //"WAVE" big endian
$Subchunk1ID_ = array(0x66, 0x6D, 0x74, 0x20); //"fmt" big endian
$AudioFormat_ = array(0x1, 0x0); //PCM = 1 little endian
$Stereo_ = array(0x2, 0x0); //Stereo = 2 little endian
$Mono_ = array(0x1, 0x0); //Mono = 1 little endian
$SampleRate_ = array(0x44, 0xAC, 0x0, 0x0); //44100 little endian
$BitsPerSample_ = array(0x10, 0x0); //16 little endian
$Subchunk2ID_ = array(0x64, 0x61, 0x74, 0x61); //"data" big endian
$files = array("C:＼＼Inetpub＼＼wwwroot＼＼Test＼＼PHP＼＼1.wav",
"C:＼＼Inetpub＼＼wwwroot＼＼Test＼＼PHP＼＼2.wav");
$Stitcher = new CStitcher();
$file = new FILESTRUCT();
$Stitcher->StitchFiles($file, $files);
可用以下代码将二进制数据写到HTTP输出中：
header(’Content-type: audio/x-wav’, true);
header(’Content-Disposition: attachment;filename=stitch.wav’);
foreach($file->ChunkID as $val) {
print chr($val);
}
foreach($file->ChunkSize as $val) {
print chr($val);
}
foreach($file->Format as $val) {
print chr($val);
}
foreach($file->Subchunk1ID as $val) {
print chr($val);
}
foreach($file->Subchunk1Size as $val) {
print chr($val);
}
foreach($file->AudioFormat as $val) {
print chr($val);
}
foreach($file->NumChannels as $val) {
print chr($val);
}
foreach($file->SampleRate as $val) {
print chr($val);
}
foreach($file->ByteRate as $val) {
print chr($val);
}
foreach($file->BlockAlign as $val) {
print chr($val);
}
foreach($file->BitsPerSample as $val) {
print chr($val);
}
foreach($file->Subchunk2ID as $val) {
print chr($val);
}
foreach($file->Subchunk2Size as $val) {
print chr($val);
}
foreach($file->Data as $val) {
print chr($val);
}
以下是一段HTML代码，用于测试结果：
<html>
<head>
<sc
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