经常用IIS作为下载服务器的时候有时传上去的文件比如 example.mp4 文件名上传后，但是用http打开的时候确显示为 404 文件不存在。其实是IIS对文件的一种保护，不在IIS指定的MIME类型里的文件不会被操作。
常见的有 mp4 / flv / iso / 7z / apk 等扩展名的文件， iis 本身是没有指定MIME类型的，这类文件默认在IIS里是不能下载的，如确需下载，则需手动添加对应的 MIME 类型。
方法如下：
- 打开IIS，在右侧找到 MIME类型
比如我们需要IIS支持 MP4 文件下载可以这么设置：（这里我们对IIS全局进行设置、如果只针对某一个站点可以直接设置站点的）
-
选中指定网站→在右侧找到 MIME类型 → 双击进入已有类型页 → 点击最右侧添加
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在弹出的 MIME类型框上 扩展名 MP4 MIME类型为： application/octet-stream
这样IIS就可以支持 MP4下载了。
下面列出一些常用的 扩展名的 MIME类型。
如果不知道MIME类型 可以写通用的: application/octet-stream
还有一些规律如果是文本类的让IE可以直接打开的 MIME 可以为 text/扩展名
如果是音频打开的时候让windows自动播放的可以用 audio/扩展名
扩展名类型/子类型 application/octet-stream 323 text/h323 acx application/internet-property-stream ai application/postscript aif audio/x-aiff aifc audio/x-aiff aiff audio/x-aiff asf video/x-ms-asf asr video/x-ms-asf asx video/x-ms-asf au audio/basic avi video/x-msvideo axs application/olescript bas text/plain bcpio application/x-bcpio bin application/octet-stream bmp image/bmp c text/plain cat application/vnd.ms-pkiseccat cdf application/x-cdf cer application/x-x509-ca-cert class application/octet-stream clp application/x-msclip cmx image/x-cmx cod image/cis-cod cpio application/x-cpio crd application/x-mscardfile crl application/pkix-crl crt application/x-x509-ca-cert csh application/x-csh css text/css dcr application/x-director der application/x-x509-ca-cert dir application/x-director dll application/x-msdownload dms application/octet-stream doc application/msword dot application/msword dvi application/x-dvi dxr application/x-director eps application/postscript etx text/x-setext evy application/envoy exe application/octet-stream fif application/fractals flr x-world/x-vrml gif image/gif gtar application/x-gtar gz application/x-gzip h text/plain hdf application/x-hdf hlp application/winhlp hqx application/mac-binhex40 hta application/hta htc text/x-component htm text/html html text/html htt text/webviewhtml ico image/x-icon ief image/ief iii application/x-iphone ins application/x-internet-signup isp application/x-internet-signup jfif image/pipeg jpe image/jpeg jpeg image/jpeg jpg image/jpeg js application/x-javascript latex application/x-latex lha application/octet-stream lsf video/x-la-asf lsx video/x-la-asf lzh application/octet-stream m13 application/x-msmediaview m14 application/x-msmediaview m3u audio/x-mpegurl man application/x-troff-man mdb application/x-msaccess me application/x-troff-me mht message/rfc822 mhtml message/rfc822 mid audio/mid mny application/x-msmoney mov video/Quicktime movie video/x-sgi-movie mp2 video/mpeg mp3 audio/mpeg mpa video/mpeg mpe video/mpeg mpeg video/mpeg mpg video/mpeg mpp application/vnd.ms-project mpv2 video/mpeg ms application/x-troff-ms mvb application/x-msmediaview nws message/rfc822 oda application/oda p10 application/pkcs10 p12 application/x-pkcs12 p7b application/x-pkcs7-certificates p7c application/x-pkcs7-mime p7m application/x-pkcs7-mime p7r application/x-pkcs7-certreqresp p7s application/x-pkcs7-signature pbm image/x-portable-bitmap pdf application/pdf pfx application/x-pkcs12 pgm image/x-portable-graymap pko application/ynd.ms-pkipko pma application/x-perfmon pmc application/x-perfmon pml application/x-perfmon pmr application/x-perfmon pmw application/x-perfmon pnm image/x-portable-anymap pot, application/vnd.ms-powerpoint ppm image/x-portable-pixmap pps application/vnd.ms-powerpoint ppt application/vnd.ms-powerpoint prf application/pics-rules ps application/postscript pub application/x-mspublisher qt video/quicktime ra audio/x-pn-realaudio ram audio/x-pn-realaudio ras image/x-cmu-raster rgb image/x-rgb rmi audio/mid roff application/x-troff rtf application/rtf rtx text/richtext scd application/x-msschedule sct text/scriptlet setpay application/set-payment-initiation setreg application/set-registration-initiation sh application/x-sh shar application/x-shar sit application/x-stuffit snd audio/basic spc application/x-pkcs7-certificates spl application/futuresplash src application/x-wais-source sst application/vnd.ms-pkicertstore stl application/vnd.ms-pkistl stm text/html svg image/svg+xml sv4cpio application/x-sv4cpio sv4crc application/x-sv4crc swf application/x-shockwave-flash t application/x-troff tar application/x-tar tcl application/x-tcl tex application/x-tex texi application/x-texinfo texinfo application/x-texinfo tgz application/x-compressed tif image/tiff tiff image/tiff tr application/x-troff trm application/x-msterminal tsv text/tab-separated-values txt text/plain 再添几个常用的 apk application/vnd.android.package-archive MRP文件（国内普遍的手机） .mrp application/octet-stream IPA文件(IPHONE) .ipa application/iphone-package-archive .deb application/x-debian-package-archive APK文件(安卓系统) .apk application/vnd.android.package-archive CAB文件(Windows Mobile) .cab application/vnd.cab-com-archive XAP文件(Windows Phone 7) .xap application/x-silverlight-app SIS文件(symbian平台/S60V1) .sis application/vnd.symbian.install-archive *（下有） SISX文件(symbian平台/S60V3/V5) .sisx application/vnd.symbian.epoc/x-sisx-app
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