参考资料: https://www.jianshu.com/p/fecdec504ab0?from=singlemessage
默认情况下， ThinkPHP downloa助手函数不支持Range header，而Safari会对video中的文件首先请求一次range:0-1，如果服务器端不支持，那么就无法播放了。
解决方法如下:
public function file($url) {
if (!session('user')) {
$this->ajaxReturn(["auth" => "timeout"]);
}
$file = \think\facade\Filesystem::path($url);
if(!isset($_SERVER['HTTP_RANGE'])) return download($file);
$ext = pathinfo($file, PATHINFO_EXTENSION);
$total = filesize($file);
$range = str_replace('=','-',$_SERVER['HTTP_RANGE']);
$range = explode('-',$range);
if (isset($range[2]) && intval($range[2]) >0){
$end = trim($range[2]);
}else{
$end = $total-1;
}
$start = trim($range[1]);
$size = $end-$start+1;
header('Content-Length:'.$size);
header('Content-Range: bytes '.$start.'-'.$end.'/'.$total);
header('Accenpt-Ranges: bytes');
if (strtolower($ext) == "mp4") header('Content-Type: video/mp4');
$fp = fopen($file,'rb+');
fseek($fp,$start);
while(!feof($fp)) {
print(fread($fp,$size));
flush();
ob_flush();
}
fclose($fp);
}