File Format Reference

HEIC is the default photo format used by every iPhone and iPad since iOS 11 (2017). It produces files roughly 50% smaller than JPEG at comparable quality, which is why Apple adopted it. The catch: almost nothing outside the Apple ecosystem can open it.

WebP is Google's open-source image format, designed to replace JPEG and PNG on the web. It produces files 25–35% smaller than equivalent JPEG or PNG images, supports transparency, and is supported by all modern browsers. The gap is everywhere else: image editors, messaging apps, and desktop software lag behind.

AVIF is the newest widely-deployed image format, based on the AV1 video codec. It achieves 40–50% smaller file sizes than PNG and outperforms WebP by around 20% — at the cost of slower encoding and incomplete software support. It's the future of web images, but not yet universal.

JPG is the image format that everyone uses without thinking about it — every photo on your phone, every product image on Amazon, every photo in a newspaper. It's so universal it's essentially invisible. Understanding how JPEG compression works and when not to use JPG helps you make better decisions about image quality and file size.

PNG is the lossless image format that replaced GIF in 1996 — it supports true colour, transparency, and exact pixel reproduction. It's the right format for logos, screenshots, icons, and anything with sharp edges or text. The downside is file size: a PNG photo can be 10× larger than a JPG. Knowing when to use PNG and when not to saves significant storage and bandwidth.

GIF is the 35-year-old format that refuses to die — it's the only animated image format that auto-plays without user interaction in every email client, Slack workspace, GitHub issue, and messaging app on earth. Understanding GIF's massive technical limitations helps you use it correctly and know when to switch to a more efficient alternative.

SVG is fundamentally different from every other image format — instead of storing pixels, it stores mathematical descriptions of shapes, paths, and text. The result: SVG images are infinitely scalable with no quality loss, tiny file sizes for simple graphics, and fully editable in code. But SVG has compatibility gaps where PNG or PDF are needed.

TIFF is the format of professional photography, print production, and document archiving. It stores images without lossy compression at any bit depth, supports multiple pages in one file, and is accepted by virtually every professional imaging workflow. For everyday use, it's overkill — but in the contexts where it's required, nothing else will do.

ICO is the format behind every favicon, every Windows application icon, and every taskbar icon. It's a container that holds multiple image sizes in one file, allowing Windows and browsers to pick the right size for the context. Here's everything you need to know about ICO and how to create favicon.ico files from PNG or SVG.

BMP is Windows's original image format — uncompressed, simple, and enormous. It predates the web, digital cameras, and virtually every modern image format. Today BMP appears mainly from Windows screenshot tools, old painting software, and certain hardware devices. If you have a BMP file, converting to JPG or PNG gives you the same image in a fraction of the file size.

EPS is the vector format of professional printing — you'll encounter it in stock photo libraries, logo files from designers, and print-production workflows. It's a PostScript-based format that was the industry standard before PDF took over. Today EPS is mostly legacy content that needs to be converted to PNG or PDF for modern use.

ARW is Sony's RAW photo format — used by Sony Alpha cameras (A7, A6000, RX100 series, and many more). RAW files contain the full unprocessed sensor data, giving photographers maximum editing latitude in Lightroom, Capture One, or Photoshop. When you need to share, post, or print ARW photos, you need to convert or export to JPG.

DNG (Digital Negative) is Adobe's open-standard RAW format — a single universal format designed to replace the dozens of proprietary RAW formats from Canon, Nikon, Sony, and other camera makers. It stores the full unprocessed sensor data from your camera, giving you maximum editing latitude in Lightroom, Photoshop, and any RAW-capable editor. When you need to share or upload DNG photos, you'll need to convert them to JPG or PNG first.

CR2 is Canon's proprietary RAW format used by Canon DSLR cameras from the EOS Rebel to the professional EOS 5D series. Like all RAW formats, CR2 captures the full unprocessed data from the camera sensor — giving photographers far more editing latitude than an in-camera JPEG would allow. To share or upload CR2 photos, you need to convert them to JPG, PNG, or another web-compatible format.

A .jfif file is a JPEG image with an unusual extension. JFIF stands for JPEG File Interchange Format — it's the original container specification that standardised how JPEG images are stored. The image data is byte-for-byte identical to a .jpg file. The only problem is compatibility: Windows doesn't open .jfif files by default, and most upload forms reject them. Converting JFIF to JPG takes seconds and fixes every compatibility issue.

RAW is not a single format — it's a category of formats. Every camera manufacturer has their own proprietary RAW format: Canon uses CR2/CR3, Nikon uses NEF, Sony uses ARW, Fujifilm uses RAF. What they all share: they contain the unprocessed data captured by the camera sensor, before any colour correction, sharpening, noise reduction, or compression is applied. RAW is the digital equivalent of a film negative.

PSD is Adobe Photoshop's native file format — the working file that holds all the layers, adjustments, masks, and edits that make up a Photoshop project. Unlike JPG or PNG (which are flat images), PSD files contain the full edit history and layer structure. They're large, complex, and can only be fully opened in Photoshop and a few other high-end applications.

AI is Adobe Illustrator's native file format — it stores vector artwork with full Illustrator feature support: multiple artboards, text as editable layers, gradients, effects, and precise typography controls. Like PSD for Photoshop, AI is a working file format, not a delivery format. When you need to share AI artwork, you convert it to PDF, SVG, or PNG.

APNG extends the PNG format with animation support — think of it as animated GIF but with PNG quality. APNG supports 24-bit colour (vs GIF's 256-colour palette), transparency without the rough edges GIF creates, and significantly better image quality for animated graphics. All major browsers support APNG, and it's the format used for animated emoji on some platforms.

JPEG XL (JXL) is the most ambitious next-generation image format — designed to eventually replace both JPEG and PNG. It achieves better compression than WebP and AVIF, supports lossless recompression of existing JPEG files (with zero quality loss, just smaller files), and has features far beyond any existing format. The catch: browser support is limited and its future is uncertain after Chrome dropped JXL support in 2022 (then the decision was reversed).

JPEG 2000 is a compression standard developed in 2000 as a technically superior successor to JPEG. It uses wavelet transforms instead of DCT blocks, producing fewer artefacts at high compression, native lossless mode, and progressive loading. Despite its technical advantages, JPEG 2000 never replaced JPEG in mainstream web use. It remains the professional standard in cinema (JPEG 2000 is the codec behind DCP — the digital cinema package), medical imaging, and archival workflows.

HEIF (High Efficiency Image File Format) is the container standard that holds HEIC images. Think of HEIF as the box and HEIC as what's inside — an image encoded with the HEVC (H.265) video codec. HEIF was standardised by MPEG in 2015 and became the default iPhone photo format in iOS 11. It delivers superior image quality at roughly half the file size of JPEG, supporting wide colour, HDR, transparency, and multi-image sequences.

NEF (Nikon Electronic Format) is Nikon's proprietary RAW image format used across all Nikon DSLR and Z-series mirrorless cameras. Like all RAW formats, NEF files contain unprocessed sensor data giving photographers maximum control over white balance, exposure, and color grading in post-production. NEF files range from 12 to 45+ MB depending on camera resolution and compression settings.

TGA (Truevision TARGA) is a raster image format from 1984 that has outlived its contemporary formats largely because of its entrenched position in game development and 3D rendering pipelines. TGA files support RGBA images (including full alpha channel transparency), store data uncompressed or with basic RLE compression, and are trivially simple to parse in code — making them a favorite for texture maps in game engines and render outputs from 3D software.

ORF is the proprietary RAW format used by Olympus cameras (now OM System). Like all RAW formats, ORF contains minimally processed sensor data — the raw photons captured by the sensor before any in-camera JPEG processing. ORF files preserve maximum dynamic range and detail for post-processing in Lightroom, Capture One, or Olympus Workspace.

RW2 is Panasonic's proprietary RAW image format, used in Lumix cameras (both MFT and L-Mount full-frame systems). Like all RAW formats, RW2 stores minimally processed sensor data for maximum editing latitude in Lightroom, Capture One, or Panasonic Lumix Lab. The format preserves everything the sensor captured — recoverable shadows, clipped highlights, and full colour information.

OpenEXR (.exr) is the industry-standard high-dynamic-range image format used in film VFX, 3D rendering, and HDR photography. Developed by Industrial Light & Magic in 1999 and open-sourced in 2003, EXR can store 16-bit or 32-bit floating-point pixel values — capturing the full luminance range of real-world scenes far beyond what 8-bit JPG or PNG can represent.

Opus is a modern open-source audio codec developed by Xiph.org and Mozilla. It powers voice and audio in Discord, Zoom, Google Meet, and every WebRTC application. It delivers remarkable audio quality at very low bitrates — outperforming MP3 at every bitrate — but almost no consumer software plays .opus files outside a browser.

MP3 is the world's most recognized audio format — it's the format that made digital music portable and powered the entire era of iPods, music downloads, and online audio. Despite being introduced in 1993, MP3 remains the universal audio format: every device, every app, every platform plays MP3. Understanding when to use it — and when to choose something better — is basic audio literacy.

WAV is the gold standard for audio recording and editing — completely uncompressed, mathematically lossless, and perfectly suited for professional audio work. The tradeoff is file size: a single minute of CD-quality WAV audio is about 10 MB. Understanding when WAV is necessary and when a compressed format is better is the key to efficient audio workflow.

M4A is Apple's audio format — used by iTunes since 2003, the default format for Apple Music purchases, and the container for podcast audio on Apple Podcasts. It typically uses AAC compression, which is technically better than MP3 at every bitrate. But M4A's compatibility is narrower than MP3, which is why converting to MP3 is sometimes necessary.

FLAC is the preferred lossless audio format for audiophiles, music archives, and anyone who wants mathematically perfect audio at roughly half the size of uncompressed WAV. If you care about audio quality and storage efficiency, FLAC is the format of choice — with the caveat that Apple devices and iTunes don't support it natively.

AAC is the audio codec that powers iTunes, YouTube, Spotify, and most modern streaming services — it's better than MP3 at every bitrate, yet most people have no idea they're listening to it. Understanding AAC helps you make better choices about audio quality, file formats, and compatibility.

WMA (Windows Media Audio) is Microsoft's proprietary audio format — the default format for Windows Media Player and Windows voice recordings throughout the 2000s and early 2010s. WMA produces smaller files than MP3 at similar perceived quality, but its compatibility with iPhones, Macs, and most portable hardware is poor. Converting WMA to MP3 makes your audio playable on every device.

AIFF (Audio Interchange File Format) is Apple's uncompressed lossless audio format — the macOS equivalent of WAV. It stores CD-quality and higher audio without any compression, making it the format of choice for professional music production, podcasting, and audio mastering. Logic Pro, GarageBand, Final Cut Pro, and Pro Tools all work natively with AIFF. For sharing or streaming, convert AIFF to MP3 or AAC.

OGG Vorbis is the open-source alternative to MP3 — royalty-free, technically superior compression, and the format Spotify uses to deliver music to your ears. But OGG has serious compatibility gaps: iPhone doesn't play it natively, car stereos usually don't support it, and many consumer audio devices have no idea what to do with a .ogg file.

MIDI files are not audio recordings — they're musical instructions. A MIDI file tells synthesizers what notes to play, at what velocity, on what instrument, for how long. The actual sound depends entirely on the synthesizer that plays it. This distinction is fundamental: a MIDI of Beethoven's Fifth Symphony might sound like a grand piano on one system and a toy keyboard on another.

AC3 (Dolby Digital) is the surround sound audio format used in DVDs, Blu-rays, digital TV broadcasts, and many video containers (MKV, VOB). It supports up to 5.1 channels of audio (front left, front center, front right, surround left, surround right, and low frequency effects/subwoofer). Understanding AC3 matters when converting video files that contain AC3 audio tracks.

ALAC is Apple's lossless audio format, stored inside an .m4a container — the same container used for AAC. It preserves 100% of the original audio data while compressing file size by 30–50% compared to uncompressed WAV or AIFF. ALAC is the lossless format of choice for Apple Music's Lossless tier, iTunes CD ripping, and audiophiles who want bit-perfect audio within the Apple ecosystem.

DTS (Digital Theater Systems) is a family of lossy and lossless surround sound audio formats found in commercial cinemas, DVDs, Blu-rays, and game consoles. The original DTS codec operates at up to 1.5 Mbps — over twice the bitrate of standard Dolby Digital — while DTS-HD Master Audio is fully lossless. DTS is particularly popular for action movies and music Blu-rays where high-fidelity multichannel audio matters.

APE is a lossless audio format created by Matthew Ashland and released in 2000 under the brand name 'Monkey's Audio.' It achieves the highest compression ratios among popular lossless codecs — APE files are typically 10–20% smaller than equivalent FLAC files. The trade-off is slow encoding/decoding, limited hardware support, and a non-open-source license. APE is primarily found in older audiophile communities and Eastern European music sharing circles.

M3U (MP3 URL) is a plain-text playlist format that lists audio or video files — either as local file paths or internet streaming URLs. Originally developed by Nullsoft for Winamp in the late 1990s, M3U became the universal playlist format supported by virtually every media player. An M3U file doesn't contain any audio or video data — it's just a text file with a list of locations. The format is used for local music playlists, internet radio streams, IPTV channel lists, and podcast feeds. M3U8 is the UTF-8 variant of M3U, used extensively in HLS (HTTP Live Streaming) for video streaming.

M4B is Apple's audiobook format — essentially an M4A (AAC audio in MPEG-4 container) file with audiobook-specific features: chapter markers, bookmarking (so you can stop and resume), and special handling in iTunes and Apple Books. M4B is the native format for audiobooks purchased from Audible (via Apple's ecosystem) and distributed through Apple Books. If you create or distribute audiobooks for Apple devices, M4B is the standard format.

AMR (Adaptive Multi-Rate) is the standard audio codec used for voice calls and voice recordings on mobile phones. It's optimised entirely for human speech — delivering intelligible voice quality at very low bitrates (4.75–12.2 kbps), making it ideal for GSM calls, voicemail, and voice memos on older smartphones. Android devices (especially older Samsung, HTC, and LG phones) often save voice recordings as AMR files. If you've received a voice message you can't play, it's probably AMR.

CAF (Core Audio Format) is Apple's professional audio container format designed to overcome the 4 GB file size limit of WAV and AIFF while providing flexible codec support. CAF is used by iOS and macOS for long voice recordings, audio development work, and applications that need to store large audio files. CAF files appear as voice recordings from certain iOS apps, outputs from Core Audio framework applications, and in some game audio pipelines targeting Apple platforms.

DSF is Sony's container for DSD (Direct Stream Digital) audio — the same 1-bit, high-sample-rate format used on Super Audio CDs (SACD). At 2.8 MHz (DSD64) or 5.6 MHz (DSD128) sample rates, it captures more high-frequency content than any PCM format. DSF is the audiophile format of choice for native DSD playback.

WavPack (.wv) is a free, open-source lossless audio compression format with a unique hybrid mode: a lossy base file (.wv) paired with a correction file (.wvc) that together reconstruct the original losslessly. The lossy-only .wv is a valid, standalone compressed audio file — an unusual design that gives WavPack maximum flexibility.

EAC-3 (Enhanced AC-3), also marketed as Dolby Digital Plus, is the modern evolution of Dolby's AC-3 codec. It powers the audio on Netflix, Disney+, Amazon Prime Video, and HBO Max. EAC-3 supports up to 7.1 channels at much higher bitrates than its predecessor, and forms the transport layer for Dolby Atmos object-based audio metadata.

TTA (True Audio) is a free, open-source lossless audio codec developed in 2004 as an alternative to FLAC. It achieves slightly better compression ratios than FLAC at its default settings and encodes/decodes very quickly. TTA never gained widespread adoption — FLAC's ecosystem is vastly larger — but a small community of audiophiles and software developers maintain it.

AU (Sun Audio) is the audio format developed by Sun Microsystems for early Unix workstations and Java applets. From the late 1980s through the early 2000s, AU was the standard sound format on Solaris, NeXTSTEP, and Java-based applications. Today it's almost entirely legacy — mostly encountered when accessing archived academic, scientific, or Java applet audio.

M4R is the iPhone ringtone format. Technically it's identical to M4A — AAC audio in an MPEG-4 container — but iOS recognizes the .m4r extension as a ringtone and adds the file to the iPhone's Ringtone library. Same audio inside, different routing in the operating system.

MKA is Matroska's audio-only container — the same flexible container as MKV without the video tracks. It can hold virtually any audio codec (FLAC, AAC, Opus, AC-3, DTS, Vorbis, MP3) and supports multiple audio tracks, chapter markers, embedded subtitles for audiobooks, and rich metadata. MKA is popular for audiobook distributions, multi-language audio, and audiophile multi-track releases.

AAX is Audible's DRM-protected audiobook format. Every audiobook downloaded from Audible's app or website comes as AAX, designed to play only in Audible's apps and authorized devices. The format includes high-quality AAC audio, chapter markers, and Whispersync metadata for cross-device read position sync. Converting AAX to MP3 or M4B requires your account's activation bytes.

MP2 (MPEG-1 Audio Layer II) is the audio codec used in DVDs, broadcast television, and DAB digital radio. It's the predecessor to MP3 (Layer III) — same MPEG-1 family but earlier in the standardization process. MP2 produces good quality at 192–384 kbps but is less efficient than MP3 at lower bitrates.

Speex is an open-source, royalty-free audio codec optimized for voice. Developed by Xiph.org from 2002, Speex was used in early VoIP applications, voicemail systems, and ham radio software. The Xiph.org Foundation officially deprecated Speex in 2012 in favor of Opus, which provides better quality across the full audio range. Speex files (.spx) are now a rarely-encountered legacy format.

XSPF (pronounced 'spiff', for Xiph.org Shareable Playlist Format) is an open-standard XML-based playlist format. It was designed to overcome limitations of the older M3U format — specifically, M3U's lack of metadata, encoding ambiguity, and weak structure. While XSPF is technically superior to M3U, it never achieved widespread adoption; M3U and PLS remain the dominant playlist formats in 2026.

M3U8 is the UTF-8 encoded variant of the M3U playlist format. While ordinary M3U files use Latin-1 (or ambiguous encoding), M3U8 explicitly uses UTF-8 to handle international characters in track names. M3U8 is also the foundation of HLS (HTTP Live Streaming), Apple's streaming protocol used by YouTube, Netflix, Twitch, and most modern video streaming services.

WebM is Google's open, royalty-free video format designed for the web. It's smaller than MP4 for streaming, supported by all modern browsers, and the format screen recorders and web-based tools often use by default. Outside the browser, support is inconsistent.

MP4 is the universal video format — it plays on every device, every browser, every platform, every smart TV. If you need video to work everywhere without hassle, it should be MP4. Understanding what's inside an MP4 file explains why it's so universal and what actually determines its quality.

AVI was the dominant video format of the 1990s and early 2000s — every movie, every downloaded video, every camcorder clip was AVI. Today it's largely obsolete, replaced by MP4. But AVI files still exist everywhere, from old hard drives to legacy software output. Here's what AVI is and the best way to convert it.

MKV is the format of choice for high-quality video storage — it supports virtually any codec, unlimited audio tracks and subtitle streams, chapter markers, and attachments. VLC plays it perfectly. Everything else might not. Here's what MKV is and when to convert it to MP4.

MOV is Apple's video container, used by iPhones, iPads, Macs, and QuickTime since 1991. Like HEIC for photos, MOV works perfectly within the Apple ecosystem but causes friction everywhere else — Windows Media Player won't open it, Android can't play it, and many video platforms reject it. Here's everything about MOV and how to convert it.

WMV is Microsoft's proprietary video format from the late 1990s — once the standard for Windows video, now largely obsolete. WMV files won't play on Mac without additional software, won't play on iPhone or Android, and are rejected by most video platforms. If you have WMV files, converting to MP4 gives them a second life with universal compatibility.

HEVC (High Efficiency Video Coding), also called H.265, is the video codec used in 4K video, modern iPhone recordings, and streaming services like Netflix and Disney+. It achieves roughly 50% better compression than H.264 at the same visual quality — meaning 4K video streams without consuming your entire data plan. The catch: older devices can't play it without stuttering, and some platforms won't accept it.

H.264, also called AVC (Advanced Video Coding), is the most widely used video codec in the world. Your iPhone videos are H.264. YouTube uses H.264. Blu-ray uses H.264. Video conference calls use H.264. Every device made in the last 15 years can play H.264 video. It's not the newest or most efficient codec, but it's the universal language of digital video.

M4V is Apple's video format used by iTunes to store movies, TV shows, and music videos. It's nearly identical to MP4 — in fact, most M4V files will play if you rename them to .mp4. The key difference: M4V files purchased from iTunes may contain Apple's FairPlay DRM (digital rights management), which restricts where you can play them. Personal videos in M4V format (like those created by Handbrake or exported by QuickTime) have no DRM and can be converted freely.

3GP is the video format created for old mobile phones — the ones that recorded shaky 176×144 pixel clips in the 2000s and early 2010s. If you have old videos from a Nokia, Sony Ericsson, early Android, or a feature phone, they're probably in 3GP. On modern phones it's essentially obsolete, but old memories come in .3gp files.

OGV is the video file format associated with the open-source Ogg container and Theora video codec. You'll encounter OGV primarily in older web projects (it was required for Firefox HTML5 video support before 2011), Linux video recordings, and open-source game engine assets. It's essentially been replaced by WebM for open-source web video.

TS (Transport Stream) files come from DVB digital TV recordings, CCTV/IP security cameras, Blu-ray disc rips, and television broadcast capture equipment. If you have a DVR that records TV programs or a security camera system, the recordings are probably .ts files. They're not compatible with most consumer video software but convert to MP4 easily.

FLV (Flash Video) was the dominant web video format from the mid-2000s until HTML5 video replaced Flash around 2015. YouTube, Vimeo, and virtually every video website used FLV. If you have old video downloads from that era — YouTube rips, screencasts, webinars, streaming video captures — they're probably FLV. Flash is dead; FLV files need to be converted to MP4.

MPG files are the original digital video format from the early 1990s — you'll find them on old CD-ROMs, VCD discs, and early digital cameras. MPEG (Moving Picture Experts Group) isn't a single format but a family: MPEG-1 for VHS-quality video, MPEG-2 for DVD and broadcast TV, and MPEG-4 which evolved into the MP4 we use today. If you have old .mpg files, they almost certainly need to be converted for modern playback.

VOB files are the actual video and audio data from DVD discs — if you've browsed a DVD's VIDEO_TS folder, you've seen them. They contain MPEG-2 video plus Dolby Digital (AC3) or MPEG audio. VOB files from your own DVDs can be converted to MP4 for storage, playback on modern devices, and archiving your DVD collection.

M2TS files are the video container used on Blu-ray discs — the AVCHD format used by camcorders and the main video format in a Blu-ray disc's BDMV/STREAM/ folder. They contain high-definition H.264 or H.265 video plus lossless audio (DTS-HD Master Audio, Dolby TrueHD) and Blu-ray PGS subtitle streams. Like VOB files for DVD, M2TS files store the actual video data of a Blu-ray.

3G2 (3GPP2) is a video container format developed by the 3rd Generation Partnership Project 2 (3GPP2) for CDMA mobile phones — specifically Verizon and Sprint devices in the US and KDDI in Japan. It's the CDMA counterpart to 3GP, which was used by GSM phones. Like 3GP, 3G2 was designed for the bandwidth limitations of early 3G networks. It's now obsolete, replaced by MP4 on all modern smartphones, but you may encounter 3G2 files from old phone recordings.

MTS (also called M2TS or AVCHD) is the video format used by high-definition consumer and prosumer camcorders from Sony, Panasonic, Canon, and others since 2006. AVCHD (Advanced Video Codec High Definition) uses H.264 video compression inside an MPEG-2 Transport Stream (MTS/M2TS) container, recording directly to SD cards, internal flash memory, or DVD discs. MTS delivers HD quality (720p, 1080i, 1080p) at manageable file sizes, making it the dominant camcorder format for about a decade before manufacturers transitioned to MP4-based recording.

MXF (Material eXchange Format) is the professional video container format used by broadcast cameras, television networks, and post-production facilities worldwide. It's the native format for Sony XDCAM cameras, Panasonic P2 cameras, Avid media, and delivery to broadcast networks including the BBC, NBC, and NHK. Unlike MP4 or MKV which target consumer use, MXF is engineered for broadcast workflows with precise timecode, multi-track audio, and complex metadata.

RM is RealNetworks' proprietary streaming video container from the late 1990s and 2000s. RealMedia files (.rm, .rmvb for variable bitrate) were ubiquitous in the dial-up streaming era — RealPlayer was the dominant video platform before Flash and YouTube arrived. Today RM files are legacy artifacts that most modern players cannot open without special codecs.

F4V is Adobe's Flash-era video container — essentially an ISO Base Media File Format (MP4 family) variant with additional Adobe-specific boxes for Flash Player streaming. F4V files look like MP4 but carry Adobe metadata that confuses standard MP4 players. With Flash Player end-of-life in 2020, F4V files are pure legacy.

ASF (Advanced Systems Format, also called Advanced Streaming Format) is Microsoft's multimedia container that houses WMV video and WMA audio. Every .wmv and .wma file is technically an ASF container. ASF was engineered for HTTP and RTSP streaming over the Windows Media Services infrastructure of the early 2000s.

RMVB (RealMedia Variable Bitrate) is an extension of the RealMedia (.rm) format that uses variable bitrate encoding instead of constant bitrate. This gave RMVB better quality-to-file-size ratio than RM at the expense of less predictable streaming behaviour. RMVB was enormously popular on Chinese video sharing sites in the 2000s — Chinese internet users distributed entire film libraries in RMVB format.

EPUB is the open-standard ebook format used by Apple Books, Kobo, Google Play Books, and most non-Kindle ereaders. It wraps HTML, CSS, and images into a single file that reflows to fit any screen size. It is the ebook equivalent of HTML — adaptable, open, and widely supported, except on Kindle.

PPTX is the format behind every PowerPoint presentation — slide decks for meetings, lectures, pitch decks, and training materials. It's an open XML format like DOCX, meaning it's technically open but most compatible with Microsoft Office. Here's when to keep it as PPTX and when to convert to PDF.

Apple Pages (.pages files) are the document format for Apple's word processor — excellent within the Apple ecosystem, essentially invisible everywhere else. Windows, Android, and Linux have no native way to open .pages files. Here's what .pages files actually are and how to convert them to PDF or DOCX.

PDF is the format that makes documents portable — identical appearance on every device, every printer, every platform. Created by Adobe in 1993 and now an open ISO standard, PDF is the universal language of documents. Understanding what PDF can and can't do helps you work with it more effectively.

DOCX is the native format of Microsoft Word and the de facto standard for editable text documents in business and academia. It's an open XML format that any compatible word processor can open — but its appearance varies between applications, which is why converting to PDF is standard before sharing finished documents.

RTF (Rich Text Format) is Microsoft's older document format that predates both DOC and DOCX. Unlike those formats, RTF is designed for cross-platform compatibility — virtually every word processor on every operating system can open it. It's the document equivalent of a lossless audio format: slightly larger than necessary, but universally readable.

XLSX is the modern Microsoft Excel spreadsheet format used by Excel 2007 and later. It's an open standard (ISO/IEC 29500) based on XML, making it readable by multiple applications — Google Sheets, LibreOffice Calc, Apple Numbers, and more. Understanding XLSX helps you work more effectively across applications and troubleshoot compatibility issues.

CSV (Comma-Separated Values) is the simplest and most universal format for exchanging tabular data. No software can't read it, no database can't import it, and no programming language lacks CSV support. CSV is the lowest common denominator of data — which is both its greatest strength and its biggest weakness.

ZIP is the world's most common archive format — a container that bundles multiple files and compresses them into one file for storage or sharing. Built into Windows, macOS, Linux, iOS, and Android without any software installation. ZIP is to file archiving what JPG is to images: not always the best option, but the one that works everywhere.

CBZ is a simple comic book archive format — a ZIP file renamed with a .cbz extension containing sequentially numbered image files (JPG, PNG, or WebP). Comic readers display the images in order, simulating flipping through a comic book. CBZ is one of the most widely supported comic formats, recognised by every major comic reader app on desktop, mobile, and e-readers. Its sibling format CBR uses a RAR archive instead of ZIP.

SRT (SubRip Text) is the most universally supported subtitle format — a plain-text file containing numbered subtitle entries with timecodes and text. Every video player, streaming platform, and video editor that supports external subtitles accepts SRT. It's simple, human-readable, and requires no special software to create or edit. SRT files are used for subtitles, closed captions, translated dialogue, and accessibility captions.

DOC is the binary file format used by Microsoft Word from 1997 through 2003. It was the dominant document format for offices worldwide for nearly a decade — a .doc file was simply 'a Word document.' In 2007, Microsoft replaced DOC with the XML-based DOCX format. DOC files are still widespread because billions were created before the transition, and many businesses, governments, and academic institutions still generate them. If you receive a .doc file today, it's almost certainly a legacy document that needs to be opened, read, or converted.

PPT is the binary file format used by Microsoft PowerPoint from 1997 through 2003 — the format that defined business presentations for a generation. Like DOC for Word, PPT was replaced by PPTX in 2007. PPT files are still common because millions of legacy presentations exist, and some enterprise systems, educational institutions, and government agencies still require the older format. If you encounter a .ppt file, it's a legacy presentation that most modern software can open but that would benefit from conversion to PPTX or PDF.

XLS is the binary spreadsheet format used by Microsoft Excel from 1997 through 2003 — the file format synonymous with spreadsheets for most of the 2000s. Like DOC and PPT, XLS was replaced in 2007 by XLSX, an open XML-based format. XLS files remain common because of the enormous volume of spreadsheets created before 2007, and because some financial systems, government databases, and enterprise software still export data in XLS format. If you work with legacy financial data, exports from old systems, or archived spreadsheets, you'll encounter XLS.

ODT (OpenDocument Text) is the open-standard file format for word processing documents, created by OASIS as a vendor-neutral alternative to Microsoft's proprietary formats. It's the default format for LibreOffice Writer, Apache OpenOffice Writer, and is supported by Google Docs and (with limitations) Microsoft Word. ODT is important in open-source software, European government IT systems, academic institutions, and anywhere vendor independence and open standards matter. If you work with LibreOffice or receive files from open-source software users, you'll encounter ODT.

ODS (OpenDocument Spreadsheet) is the open-standard file format for spreadsheets, part of the OpenDocument Format (ODF) family. It's the default format for LibreOffice Calc and Apache OpenOffice Calc, and is supported by Google Sheets and (with limitations) Microsoft Excel. ODS is the spreadsheet equivalent of ODT — a vendor-neutral, ISO-standardised alternative to Microsoft's XLS/XLSX formats. It's common in open-source environments, European government IT systems, and organisations committed to open standards.

RAR (Roshal Archive) is a proprietary archive format created by Eugene Roshal in 1993 — the most popular alternative to ZIP for compressed archives. RAR offers better compression ratios than ZIP, multi-volume archives, built-in error recovery, and AES-256 encryption. It's widely used for distributing large collections of files, game archives, software, and media. RAR files are ubiquitous on file-sharing platforms and Windows software distribution, though the format is proprietary (unlike ZIP).

7Z (7-Zip Archive) is an open-source archive format developed by Igor Pavlov for the 7-Zip software. It achieves the highest compression ratios of any mainstream archive format — typically 30–50% smaller than ZIP and 10–20% smaller than RAR for the same content. 7Z is free, open-source, and fully documented. It's the preferred format for software distribution, backups, and any use case where minimising archive size is the priority.

TXT (plain text) is the simplest possible document format — raw text characters with no formatting, no fonts, no images, no layout. Every operating system, every programming language, every text editor, and every era of computing can read TXT files. A TXT file created in 1970 opens perfectly in 2024. It's the universal, timeless format for any content that's just words — configuration files, code, notes, logs, data interchange, and long-term archiving.

MOBI (Mobipocket) is the original e-book format used by Amazon Kindle. Based on the PalmDOC format and developed by Mobipocket (acquired by Amazon in 2005), MOBI was Kindle's native format until Amazon introduced AZW3/KF8 and later began supporting EPUB. MOBI files are still common in e-book libraries, especially for older Kindle content and books distributed outside Amazon's store. Calibre, the universal e-book manager, handles MOBI natively.

TAR (Tape Archive) is an archive format originally designed for backing up files to magnetic tape drives on Unix systems. Unlike ZIP, TAR does not compress files by itself — it simply bundles multiple files and directories into a single archive while preserving Unix file permissions, ownership, and symbolic links. Compression is applied separately using gzip (.tar.gz or .tgz), bzip2 (.tar.bz2), or xz (.tar.xz). TAR is the standard archive format for Linux and macOS software distribution.

GZ (gzip) is a file compression format based on the DEFLATE algorithm (LZ77 + Huffman coding), created in 1992 as a free replacement for the patented Unix compress tool. A .gz file is a single file compressed with gzip — it is not an archive (TAR is). Gzip is one of the most widely used compression tools in computing: web servers use it for HTTP content-encoding (shrinking HTML/CSS/JS before sending to browsers), Linux packages use .tar.gz for distribution, and log rotation tools compress old logs to .gz to save disk space.

JSON (JavaScript Object Notation) is a lightweight text-based data format that is easy for humans to read and write, and easy for machines to parse and generate. Introduced in the early 2000s by Douglas Crockford and standardized as RFC 8259, JSON has become the universal language of web APIs, configuration files, and data exchange. It represents data as key-value pairs (objects), ordered lists (arrays), strings, numbers, booleans, and null — a simple set of types that maps naturally to data structures in virtually every programming language.

XML (Extensible Markup Language) is a text-based format for storing and transporting structured data, published as a W3C recommendation in 1998. Unlike HTML (which has fixed tags), XML lets you define your own tags to describe any kind of data. XML uses a tree structure of elements (opening and closing tags), attributes (key-value pairs inside tags), and text content. It was the dominant data format for web services and enterprise systems throughout the 2000s, and remains essential for SOAP APIs, RSS/Atom feeds, SVG images, Microsoft Office documents (DOCX, XLSX, PPTX are ZIP files containing XML), and countless configuration formats.

YAML (YAML Ain't Markup Language, originally Yet Another Markup Language) is a data serialization format designed to be readable by humans. Created in 2001, YAML uses indentation and minimal punctuation to represent data structures — no curly braces, no brackets, no quotes for simple strings. YAML is a superset of JSON (valid JSON is valid YAML), but YAML adds comments, multi-line strings, anchors and aliases (for reusing values), and multiple equivalent syntax styles. It is the standard format for Docker Compose, Kubernetes manifests, GitHub Actions, GitLab CI, Ansible playbooks, and many other DevOps tools.

KEY (Keynote) is the native file format for Apple's Keynote presentation software, part of the iWork suite. Introduced with Keynote in 2003, .key files store slides, transitions, animations, embedded media, speaker notes, and Keynote-specific design features. Modern .key files (Keynote 6+, released 2013) use an iWork Archive format — a directory package (appearing as a single file on macOS) containing a binary protobuf data file and asset folders. Keynote is pre-installed on all modern Macs and is free on iOS and iPadOS.

ASS — Advanced SubStation Alpha — is a subtitle format that goes far beyond plain text. It supports per-line font, colour, border, shadow, position, rotation, and karaoke-style character-by-character timing. Anime fansubs popularised it; today it's the default subtitle track in most MKV releases.

WebVTT (.vtt) is the W3C subtitle standard for the web. Every HTML5 <video> element supports VTT via a <track> element, and it's the required subtitle format for HLS, DASH, and most streaming CDNs. It's plain UTF-8 text that any text editor can open.

An ISO file is a sector-by-sector copy of an optical disc — a complete image of a CD, DVD, or Blu-ray. The format uses the ISO 9660 file system (also called CDFS) defined in 1988. ISO files are how operating systems are distributed, software is archived, and disc content is preserved digitally.

DMG (Apple Disk Image) is macOS's native disk image format. Mac apps are distributed as DMG files; macOS users 'mount' them by double-clicking, drag the app to Applications, and unmount. DMG supports compression, encryption, and Apple's HFS+/APFS file systems — making it more flexible than ISO for Mac workflows.

XZ is a lossless data compression format that uses the LZMA2 algorithm — the same compression engine as 7-Zip. Released in 2009 as a successor to lzma-utils, XZ achieves significantly better compression ratios than gzip and bzip2 at the cost of more CPU during compression. It's the default compression for kernel.org and many Linux distributions.

DjVu (pronounced 'déjà vu') is a digital document format developed by AT&T Labs specifically for scanned books, magazines, and academic papers. It uses sophisticated foreground/background separation to compress scanned pages dramatically — a 500-page scanned book that would be 50 MB in PDF can fit in 2 MB as DjVu. Despite its technical merits, DjVu remained niche due to lack of mainstream support.

FB2 (FictionBook 2) is an XML-based e-book format that originated in the Russian e-book community. Unlike EPUB (which is a ZIP archive), FB2 is a single XML file containing the entire book — text, formatting, metadata, and embedded images all in one structured document. The format remains popular in Eastern European and Russian-language e-book communities.

AZW3 is Amazon's current Kindle e-book format, also known as KF8 (Kindle Format 8). Introduced in 2011, AZW3 supports modern typography features that the older MOBI format couldn't handle — custom fonts, drop caps, fixed layouts for children's books and graphic novels, and CSS3 styling. Every modern Kindle book ships in AZW3 format.

VCF (vCard) is the universal contact file format used by every phone, email client, and address book on Earth. Introduced by Versit Consortium in 1995, vCard standardized how contact information (name, phone, email, address, photo) is exchanged between systems. Today, every iPhone, Android phone, Gmail, Outlook, and Contacts app reads and writes VCF files natively.

ICS (iCalendar) is the universal calendar file format used by Google Calendar, Apple Calendar, Outlook, and every modern calendaring system. Defined in RFC 5545, iCalendar standardized how calendar events are exchanged between systems. ICS files contain one or more events with full metadata — start/end times, time zones, recurrence rules, attendees, alarms, and rich descriptions.

PRC (Palm Resource Code) is a legacy e-book format from the Palm OS and pre-Kindle era. Most PRC files are actually Mobipocket format (the predecessor to MOBI and AZW3) with the .prc extension instead of .mobi. PRC was the standard for Palm OS PDAs (Palm Pilot, Treo, Sony Clié) in the early 2000s and persisted in the Mobipocket reader.