MIME 類別 (IANA 媒體類別)
媒體類別(多用途網際網路郵件擴展或是MIME類別)是一種表示文件、檔案或各式位元組的標準。它被定義並規範在IETF的 RFC 6838。
重要: 瀏覽器會採用MIME類別， 而非副檔名 ，來判定如何對URL進行處理。所以伺服器要在回應的
text。子類別(subtype) 則定義該資料精確的MIME類別。例如MIME 類別為
html (HTML 源碼), 或
There are two classes of type: discrete and multipart. Discrete types are types which represent a single file or medium, such as a single text or music file, or a single video. A multipart type is one which represents a document that's comprised of multiple component parts, each of which may have its own individual MIME type; or, a multipart type may encapsulate multiple files being sent together in one transaction. For example, multipart MIME types are used when attaching multiple files to an email.
The discrete types currently registered with the IANA are:
applicationList at IANA
- Any kind of binary data that doesn't fall explicitly into one of the other types; either data that will be executed or interpreted in some way or binary data that requires a specific application or category of application to use. Generic binary data (or binary data whose true type is unknown) is
application/octet-stream. Other common examples include
audioList at IANA
- Audio or music data. Examples include
- Reserved for use as a placeholder in examples showing how to use MIME types. These should never be used outside of sample code listings and documentation.
examplecan also be used as a subtype; for instance, in an example related to working with audio on the web, the MIME type
audio/examplecan be used to indicate that the type is a placeholder and should be replaced with an appropriate one when using the code in the real world.
fontList at IANA
- Font/typeface data. Common examples include
imageList at IANA
- Image or graphical data including both bitmap and vector still images as well as animated versions of still image formats such as animated GIF (en-US) or APNG. Common examples are
modelList at IANA
- Model data for a 3D object or scene. Examples include
textList at IANA
- Text-only data including any human-readable content, source code, or textual data such as comma-separated value (CSV) formatted data. Examples include
videoList at IANA
- Video data or files, such as MP4 movies (
For text documents without a specific subtype,
text/plain should be used. Similarly, for binary documents without a specific or known subtype,
application/octet-stream should be used.
Multipart types indicate a category of document broken into pieces, often with different MIME types; they can also be used — especially in email scenarios — to represent multiple, separate files which are all part of the same transaction. They represent a composite document.
With the exception of
multipart/form-data, used in the
POST method of HTML Forms, and
multipart/byteranges, used with
Partial Content to send part of a document, HTTP doesn't handle multipart documents in a special way: the message is transmitted to the browser (which will likely show a "Save As" window if it doesn't know how to display the document).
There are two multipart types:
messageList at IANA
- A message that encapsulates other messages. This can be used, for instance, to represent an email that includes a forwarded message as part of its data, or to allow sending very large messages in chunks as if it were multiple messages. Examples include
message/rfc822(for forwarded or replied-to message quoting) and
message/partialto allow breaking a large message into smaller ones automatically to be reassembled by the recipient.
multipartList at IANA
- Data that is comprised of multiple components which may individually have different MIME types. Examples include
multipart/form-data(for data produced using the
multipart/byteranges(defined in RFC 7233: 5.4.1 and used with HTTP's
206"Partial Content" response returned when the fetched data is only part of the content, such as is delivered using the Range (en-US) header).
這是二進制檔案的預設類別，代表未知的二進制檔案，通常瀏覽器都不執行或是會詢問是否要執行。They treat it as if the Content-Disposition (en-US) header was set to
attachment, and propose a "Save As" dialog.
text/plain 不代表"任何一種文字檔案"。例如從用於表示CSS檔案的<link> (en-US)元素載了一個
用來套用在網頁的 CSS 檔案一定要配合
.css 視為 CSS 檔案，伺服器有可能會使用
application/octet-stream 的 MIME 型態來傳輸檔案，而導致這些檔案不被大多數的瀏覽器當成 CSS 而被忽略。
All HTML content should be served with this type. Alternative MIME types for XHTML (like
application/xhtml+xml) are mostly useless nowadays.
application/xhtml+xml if you want XML’s strict parsing rules,
<![CDATA[…]]> sections, or elements that aren't from HTML/SVG/MathML namespaces.
Note: Even though any given user agent (en-US) may support any or all of these, you should only use
Some content you find may have a
charset parameter at the end of the
Files whose MIME type is
image contain image data. The subtype specifies which specific image file format the data represents. Only a few image types are used commonly enough to be considered safe for use on web pages:
|Abbreviation||File format||MIME type||File extension(s)||Summary|
|APNG||Animated Portable Network Graphics||
||Good choice for lossless animation sequences (GIF is less performant). AVIF and WebP have better performance but less broad browser support.
Supported: Chrome, Edge, Firefox, Opera, Safari.
|AVIF||AV1 Image File Format||
Good choice for both images and animated images due to high performance and royalty free image format. It offers much better compression than PNG or JPEG with support for higher color depths, animated frames, transparency etc. Note that when using AVIF, you should include fallbacks to formats with better browser support (i.e. using the
|GIF||Graphics Interchange Format||
||Good choice for simple images and animations. Prefer PNG for lossless and indexed still images, and consider WebP, AVIF or APNG for animation sequences.
Supported: Chrome, Edge, Firefox, IE, Opera, Safari.
|JPEG||Joint Photographic Expert Group image||
Good choice for lossy compression of still images (currently the most popular). Prefer PNG when more precise reproduction of the image is required, or WebP/AVIF if both better reproduction and higher compression are required.
|PNG||Portable Network Graphics||
PNG is preferred over JPEG for more precise reproduction of source images, or when transparency is needed. WebP/AVIF provide even better compression and reproduction, but browser support is more limited.
|SVG||Scalable Vector Graphics||
||Vector image format; ideal for user interface elements, icons, diagrams, etc., that must be drawn accurately at different sizes.
Support: Chrome, Edge, Firefox, IE, Opera, Safari.
|WebP||Web Picture format||
||Excellent choice for both images and animated images. WebP offers much better compression than PNG or JPEG with support for higher color depths, animated frames, transparency etc. AVIF offers slightly better compression, but is not quite as well-supported in browsers and does not support progressive rendering.
Support: Chrome, Edge, Firefox, Opera, Safari
As is the case for images, HTML doesn't mandate that web browsers support any specific file and codec types for the <audio> (en-US) and <video> (en-US) elements, so it's important to consider your target audience and the range of browsers (and versions of those browsers) they may be using when choosing the file type and codecs to use for media.
Our media container formats guide provides a list of the file types that are commonly supported by web browsers, including information about what their special use cases may be, any drawbacks they have, and compatibility information, along with other details.
The audio codec and video codec guides list the various codecs that web browsers often support, providing compatibility details along with technical information such as how many audio channels they support, what sort of compression is used, and what bit rates and so forth they're useful at. The codecs used by WebRTC guide expands upon this by specifically covering the codecs supported by the major web browsers, so you can choose the codecs that best cover the range of browsers you wish to support.
As for MIME types of audio or video files, they typically specify the container format (file type). The optional codecs parameter can be added to the MIME type to further specify which codecs to use and what options were used to encode the media, such as codec profile, level, or other such information.
The most commonly used MIME types used for web content are listed below. This isn't a complete list of all the types that may be available, however. See the media container formats guide for that.
|MIME type||Audio or video type|
||An audio file in the WAVE container format. The PCM audio codec (WAVE codec "1") is often supported, but other codecs have limited support (if any).|
||An audio file in the WebM container format. Vorbis and Opus are the codecs officially supported by the WebM specification.|
||A video file, possibly with audio, in the WebM container format. VP8 and VP9 are the most common video codecs; Vorbis and Opus the most common audio codecs.|
||An audio file in the Ogg container format. Vorbis is the most common audio codec used in such a container; however, Opus is now supported by Ogg as well.|
||A video file, possibly with audio, in the Ogg container format. Theora is the usual video codec used within it; Vorbis is the usual audio codec, although Opus is becoming more common.|
||An audio or video file using the Ogg container format. Theora is the usual video codec used within it; Vorbis is the usual audio codec.|
multipart/form-data type can be used when sending the values of a completed HTML Form from browser to server.
As a multipart document format, it consists of different parts, delimited by a boundary (a string starting with a double dash
--). Each part is its own entity with its own HTTP headers, Content-Disposition (en-US), and
Content-Type for file uploading fields.
Content-Type: multipart/form-data; boundary=aBoundaryString (other headers associated with the multipart document as a whole) --aBoundaryString Content-Disposition: form-data; name="myFile"; filename="img.jpg" Content-Type: image/jpeg (data) --aBoundaryString Content-Disposition: form-data; name="myField" (data) --aBoundaryString (more subparts) --aBoundaryString--
<form action="http://localhost:8000/" method="post" enctype="multipart/form-data"> <label>Name: <input name="myTextField" value="Test"></label> <label><input type="checkbox" name="myCheckBox"> Check</label> <label>Upload file: <input type="file" name="myFile" value="test.txt"></label> <button>Send the file</button> </form>
will send this message:
POST / HTTP/1.1 Host: localhost:8000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:50.0) Gecko/20100101 Firefox/50.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Connection: keep-alive Upgrade-Insecure-Requests: 1 Content-Type: multipart/form-data; boundary=---------------------------8721656041911415653955004498 Content-Length: 465 -----------------------------8721656041911415653955004498 Content-Disposition: form-data; name="myTextField" Test -----------------------------8721656041911415653955004498 Content-Disposition: form-data; name="myCheckBox" on -----------------------------8721656041911415653955004498 Content-Disposition: form-data; name="myFile"; filename="test.txt" Content-Type: text/plain Simple file. -----------------------------8721656041911415653955004498--
multipart/byteranges MIME type is used to send partial responses to the browser.
Partial Content status code is sent, this MIME type indicates that the document is composed of several parts, one for each of the requested ranges. Like other multipart types, the
Content-Type uses a
boundary to separate the pieces. Each piece has a
Content-Type header with its actual type and a Content-Range (en-US) of the range it represents.
HTTP/1.1 206 Partial Content Accept-Ranges: bytes Content-Type: multipart/byteranges; boundary=3d6b6a416f9b5 Content-Length: 385 --3d6b6a416f9b5 Content-Type: text/html Content-Range: bytes 100-200/1270 eta http-equiv="Content-type" content="text/html; charset=utf-8" /> <meta name="vieport" content --3d6b6a416f9b5 Content-Type: text/html Content-Range: bytes 300-400/1270 -color: #f0f0f2; margin: 0; padding: 0; font-family: "Open Sans", "Helvetica --3d6b6a416f9b5--
Most web servers send unrecognized resources as the
application/octet-stream MIME type. For security reasons, most browsers do not allow setting a custom default action for such resources, forcing the user to save it to disk to use it.
Some common incorrect server configurations:
RAR-compressed files. In this case, the ideal would be the true type of the original files; this is often impossible as .RAR files can hold several resources of different types. In this case, configure the server to send
Proprietary file types. Avoid using
application/octet-streamas most browsers do not allow defining a default behavior (like "Open in Word") for this generic MIME type. A specific type like
application/vnd.mspowerpointlets users open such files automatically in the presentation software of their choice.
In the absence of a MIME type, or in certain cases where browsers believe they are incorrect, browsers may perform MIME sniffing — guessing the correct MIME type by looking at the bytes of the resource.
Each browser performs MIME sniffing differently and under different circumstances. (For example, Safari will look at the file extension in the URL if the sent MIME type is unsuitable.) There are security concerns as some MIME types represent executable content. Servers can prevent MIME sniffing by sending the X-Content-Type-Options (en-US) header.
MIME types are not the only way to convey document type information:
- Filename suffixes are sometimes used, especially on Microsoft Windows. Not all operating systems consider these suffixes meaningful (such as Linux and MacOS), and there is no guarantee they are correct.
- Magic numbers. The syntax of different formats allows file-type inference by looking at their byte structure. For example, GIF files start with the
47 49 46 38 39hexadecimal value (
GIF89), and PNG files with
89 50 4E 47(
.PNG). Not all file types have magic numbers, so this is not 100% reliable either.