How2Day: Header MIME Types

When information is sent over the Internet, MIME types help to identify it. http:// (in macro) image by Igor Negovelov from Fotolia.com
MIME types, also known as Internet media types, identify the formats for media sent over the Internet. When MIME types are sent as part of the Content-type Header in Internet communications, they indicate to programs such as Web browsers how to present the media referred to. MIME types are indicated using two parts, a type and a subtype. Sometimes a parameter may also be included.

The "application" type can be accompanied by many different subtypes, including "octet-stream," which represents data in binary form. Other application subtypes include PostScript, spreadsheets in formats such as Excel, and various types of data relating to email programs. Feed formats such as Atom and JSON can also be application subtypes.

The "image" MIME type has a number of associated subtypes to represent particular image formats. Image MIME types have specific requirements in terms of how a program renders them for display, which is the primary reason for including the subtype indicator. Common image subtypes include "jpeg," "png" and "gif" for file extensions ".jpg," ".png" and ".gif" respectively.

The "text" MIME type refers to the many types of textual data that are used in Internet contexts. Subtypes of text include "plain," "html" and "css." Plain text can typically be viewed without the need for any additional programs; however, HTML and CSS are designed primarily for use within Web browsers. As with most MIME types, these subtypes indicate to a Web browser how to interpret the content of included data.

Audio MIME types require specific programs and facilities to be made accessible to users, such as speakers and audio software. Audio subtypes include the various audio file formats in use, such as "mpeg," "x-aiff" and "x-wav," representing MP3, AIFF and WAV files, respectively.

MIME subtypes within the video type have very specific requirements in terms of playback both for audio-visual output in hardware and software programs. Common video subtypes are "mpeg," "quicktime" and "x-msvideo," representing formats such as ".mpg," ".mov" and ".avi" in media files.

The "multipart" MIME type indicates that data is contained within different formats. Subtypes include "mixed," "parallel," "digest" and "alternative," indicating how the various parts should be viewed and accessed. Since a multipart MIME type indicates more than one type of data, further interpretation is normally required.

The "message" MIME type is for various formats of Internet text messages. Since MIME types occur within Internet messages, this means that the data contained may indicate a further type or subtype. The subtype "partial" is used to indicate a section of a larger message that is being sent in parts. The main subtype for message MIME types is "rfc822," which indicates that the message data conforms to the ARPA standard.

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