ZhiZe

Just ZhiZe.

11 minute read

File Format Research is a series of introductory articles about file formats I care about.

A file format is an specification that can be executed or parsed by the corresponding computing environment when the data is stored in a standardized format. Therefore, on the surface, the file format is only a specification for the format of each data file. In fact, it is also a specification for the corresponding interpreter, compiler or reading and writing tools.

These articles focus on file formats that are parsed directly as a whole by application software and presented to human directly. The format of some files in a multi-file system that do not need to be directly viewed or modified by humans has low priority.

File Format Names

Each file format has 3 names:

  • Media Type Name as the main identifier.
  • Natural Language Name is used for the article titles and paragraphs.
  • Suffix Name is used to distinguish file types in the file system.

Media Type Name

Generally, it is filled in according to the Media Type of IANA (Internet Assigned Numbers Authority). Details can be found at:

For those that cannot be found on MIME, I will find names in other websites such as Wikipedia or arrange the names myself. But this should be marked “non-standard”.

It is also possible that one file format corresponds to multiple Media Types. In this case, try to keep one or seperate them into different file types.

Natural Language Name

For convenience of natural language expression, each file format should have a natural language name. If there is a standard for this name, choose the standard. If there is no standard, choose the common name. I will choose a suitable name by yourself sometimes. It will be used as the document title when introducing the file format.

Although this name is mainly used in natural languages, there should be no duplication.

Suffix Name

The file extension is part of the file name in the file system and is used to identify the file format type. Generally speaking, the file format suffix is located at the end of the file name, starting with a period ., followed by letters or numbers.

The suffix name is mainly determined based on the recommendation of the file format standard or standards maintenance organization. If there is no recommendation, it will be generally used name. In these articles, try to ensure that a suffix name belongs to only one file format. If there is a suffix name conflict, the conflict handling method should be stated.

In addition, a file format generally has only one suffix name. When the letters in the suffix name can be uppercase or lowercase, the lowercase form is generally used. When a file format has multiple suffixes, choose the most commonly used or standardized one. It is possible that a file format have multiple suffix names. Generally speaking, a file format can identify its different variants through the meta information inside the file. It is not necessary to distinguish the variant of file format by suffix name, so currently do not give multiple suffix names to a file format. If must, sperate them into different file format types.

The suffix name will also be used as the abbreviation of the file format. When used as a file abbreviation, all capital letters (and without .)are used unless otherwise agreed.

File format type inheritance

There is an inheritance relationship between file formats. All file formats essentially derive from constraints and specifications on binary files.

When file format B inherits A, every qualified B file is required to be a qualified A file. Improved relationships between file formats are not reflected in this description. The two file formats before and after the improvement are considered to be in a parallel relationship.

If a file format inherits directly from the 8-bit binary byte format, enter “Byte” in the “Parent Format” column.

Programming languages that have corresponding file formats record corresponding file formats.

Programming languages that do not have corresponding formats are mentioned as language extensions in their main dependent languages and supplemented with reference materials and tags.

Languages that do not have independent file formats or dependent formats such as BNF are not documented in this series of articles.

Symbols and Tags

Here are descriptions of the symbols I’ll use in this series of articles:

  • Openness
    • Open Source?
      • 📖 Open format documentation
      • 📕 Private format documentation
    • Charge?
      • 🆓 Free
      • 💰 Charge

I also add at least one tag describing the usage of each format. The number of such tags is variable.

Recommendations File Format

Common Use

Archive

Optical Disc Archive
  • 🆓📖 .iso ISO: An optical disc file system image file format.
Universal File System Archive
  • 🆓📖 .7z 7Z: General archive and compression format with more function and better compression ratio than ZIP. But not many file formats use 7Z as the base format.

Read only:

  • 💰📕 .rar RAR: Archive and compression format.
  • 🆓📖 .zip ZIP: General archive and compression format, also as the basis for many other file formats.

Plain Text

Files without extensions will be treated as plain text files by default. But there is still a suffix for plain text files:

Universal Markup Data

Although these file formats can theoretically replace each other, their different syntax designs cause them to have different adaptability to different scenarios. Generally, one or more of them are selected according to the needs or framework requirements. So there are multiple alternatives juxtaposed.

Domain-specific

.NET Runtime Environment

Audio Sampling

  • 🆓📖 .aac AAC: Lossy audio sample format, but better than mp3.
  • 🆓📖 .flac FLAC: Lossless audio sample format.
  • 🆓📖 .mka Matroska Audio: Matroska audio. Used to encapsulate complex audio files or as components of other Matroska formats.

Read only:

  • 🆓📖 .mp3 MP3: Lossy audio sample format.
  • 🆓📖 .wav Waveform Audio File Format: An audio file format. It uses the linear pulse-code modulation (LPCM).

Bibliography Data

  • 🆓📖 .bib BibTeX: A data format for recording citation sources.

C Compiler Source Files

C++ Compiler Source Files

E-document Release

Electronic Display
  • 🆓📖 .epub EPUB: E-book format based on web related technologies.

Read only:

Imitating Paper
  • 🆓📖 .pdf Portable Document Format: Mainly used as document format for both scanned and rendered, sometimes used as vector image format.

Read only:

  • 🆓📖 .djvu DjVu: Document format or pixel image format for scanned documents.

Editable Document Container

Font

Read only:

  • 🆓📖 .woff WOFF: Vector font file for web.

Pixel Image

Read only:

PowerShell Runtime Environment

Python Runtime Environment

  • 🆓📖 .py Python: A general programming language.

Rust Compiler Source Files

Timed Text

  • 🆓📖 .lrc LRC: A simple lyric file format.
  • 🆓📖 .mks Matroska Subtitle: Matroska subtitle. Used to encapsulate complex subtitle files or as components of other Matroska formats.
  • 🆓📖 .srt SubRip: A plain text-based external subtitle format.

Typesetting Description

  • 🆓📖 .md Markdown: A simple markup format used to write documents without complex style or structure.
  • 🆓📖 .tex TeX: Markup language format for TeX typesetting system.

Vector Image

Video Container

  • 🆓📖 .mkv Matroska Video: Matroska video. Used to encapsulate complex audiovisual files.
  • 🆓📖 .mp4 MP4: A common audio and video container formats. Used to encapsulate relatively simple audio and video streams.

Read only:

  • 🆓📖 .avi Audio Video Interleave: An audio and video file format dominated by Microsoft.
  • 🆓📖 .flv Flash Video: An audio and video container for Adobe Flash.

Web Page Style Sheet

  • 🆓📖 .css Cascading Style Sheets: A markup language used to describe the styles of HTML elements.
  • 🆓📖 .scss SCSS: A markup language that generates CSS. It’s like an extension to SCSS.

Read only:

  • 🆓📖 .sass Sass: A markup language that generates CSS.It uses indentation to indicate code levels.

Web Page Typesetting

System Compatible File Formats

Binary File Formats for Old Version Microsoft Office

These file formats have different purposes, but are all file formats from older versions of Microsoft Office.

Delimiter-separated Values

These formats primarily use delimiter separation to represent tabular data. The readability of this type of data source code is very poor when there is a lot of data.

If you do not use a plain text editor to directly edit the table content, but use software to operate it, you do not necessarily need to use this type of format. Delimiter-seperated values are not as good as binary files in terms of compression rate, and are not as good as XML, JSON, etc. in terms of scalability and data type richness.

  • 🆓📖 .csv Comma-Separated values: A simple markup language for representing tabular data.
  • 🆓📖 .tsv Tab-Separated Values: A simple markup language for representing tabular data. Use horizontal tabs as delimiters.

OpenDocument File Formats

These are open source office document formats. But its model is modeled after Microsoft Office. If you disregard the needs and patterns defined by Microsoft Office, there are many better alternatives available. But if you must imitate Microsoft Office and be completely open source, this is currently the best option.

Unix-like System Archive and Compression

On Unix-like systems, archiving and compression are treated as two operations. Tar is responsible for archiving, and other softwares is responsible for compressing. This is a relatively complex process to use.

One advantage of these software is that Tar can save file permission information on file systems of Unix-like systems. But I personally think it’s better to include a shell script with the archive to set the file permissions. This eliminates the need to use a tar archive.

  • 🆓📖 .bz2 Bzip2: Single file compression format.
  • 🆓📖 .gz Gzip: Single file compression format.
  • 🆓📖 .tar Tar: Archive file format.
  • 🆓📖 .xz XZ: Single file compression format.

Unix-like System Shell Script

A type of shell script mainly used on Unix systems. Overall the syntax is archaic and strange. Sometimes adding an extra space before or after an operator can cause errors.

  • 🆓📖 .sh Bourne Shell: Universal system management script for Unix.
  • 🆓📖 .profile Bourne Shell Config: The file used for the initial configuration of the Bourne Shell. It is also supported by many other shells.
  • 🆓📖 .bashrc Bash Config: Script for setting up Bash.

TrueType Compatible System Font

These are mainly used for systems that don’t have good support for .otf. Such systems should be gradually reduced in the future. At that time, TrueType-flavored fonts will also use the .otf suffix.

Trend

Trends in file format recommendation changes.

  • Replace MP4 with MKV.

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