php的文件读取跟写入似乎对未知格式的文件不管用

$file="宋1.mp3.part1";
$file1="宋2.mp3.part1";
$file2="宋3.mp3.part1";
$fp = fopen($file, "a");
$fp1 = fopen($file1, "r");
$fp2 = fopen($file2, "r");
// if(!$fp1) echo "aa";
// return;
//fseek(fp, 0, SEEK_END);
$index=0;
 while(!feof($fp1)){//测试文件指针是否到了文件结束的位置 
        $content=fread($fp1,10); 
        if(fwrite($fp,$content)==false)
		echo "不能写入到文件 $filename"; 
		$index++;
		echo $index;
    } 
	$index=0;
	while(!feof($fp2)){//测试文件指针是否到了文件结束的位置 
        $content=fread($fp2,10); 
        fwrite($fp,$content); 
			$index++;
		echo $index;
    } 
    fclose($fp);  
    fclose($fp1); 
    fclose($fp2); 
	rename ($file, "a.mp3"); 
	echo "ok";
?>

$str="宋1.txt";
$str=iconv("utf-8", "GBK", $str);//注释掉就会失败
$fp = fopen($str, "a");
if(fwrite($fp,"losasds")!==false) echo "ok";
else echo "fail";
fclose($fp);