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The reference pages say what a format is. These say which one you should pick, what a conversion costs you, and what to do when a file refuses to open.
Format comparisons#
Two formats side by side, and which one the file you have should end up in.
Animated GIF vs WebP vs AVIF
GIF, WebP and AVIF can all hold an animation, but GIF locks every frame to a 256-colour palette with no partial transparency, while WebP and AVIF carry full colour and a real alpha channel.
WebP vs JPG
Use WebP for images a browser will display and JPG for files that have to open somewhere else. The size gap is wider than most sources report, and converting costs you something in both directions.
How file formats work#
The ideas underneath every conversion, explained once so the rest of the site can point at them.
Alpha Channels and Transparency
PNG, WebP, AVIF, TIFF and GIF can all store transparency; JPEG never could. Only GIF's version is binary, so a soft-edged logo saved as GIF turns jagged before you've even picked a background colour.
An EPUB Is a Zip of Web Pages
Rename any EPUB to .zip and open it, a folder of XHTML pages, CSS, images and a manifest naming the reading order. That structure is why the same file turns into a different number of pages depending on what opens it.
Bit Depth and Banding
Eight bits per channel gives you 256 shades, and a real gradient like a hazy sky can use as few as a few dozen of them, so each shade covers enough pixels to read as a stripe. Work in a higher bit depth until the final export and the stripes mostly disappear; flatten to 8-bit early and no later edit brings them back.
Chroma Subsampling, and Why Red Text Goes Fuzzy
Most encoders store colour at a fraction of the resolution they use for brightness, because an ordinary photo almost never shows the gap. A saturated edge, like red text on blue, is the one thing that does.
Codec vs Container
The container is the box, .mp4, .mkv, .mov. The codec is how the video and audio inside were actually compressed, and it's almost always the codec, not the container, that decides whether a file will play.
Colour Profiles, and Why Your Photo Changed Colour
A pixel's numbers only specify a colour once an ICC profile says what colour space they're measured against. Drop that tag on the way through a conversion and the same numbers get repainted, not preserved.
DPI, and Why It Means Nothing on a Screen
DPI is a number saved in a file's header telling a printer how large to print it. It has no effect on the pixels themselves, and a screen ignores it completely.
EXIF: What Your Photos Are Carrying
A phone photo can carry the make and model of the camera that shot it, the settings it was shot at, the exact timestamp, and the precise spot on Earth where you were standing when you pressed the shutter, and a conversion either keeps every bit of that or throws it all away depending on the format you pick.
H.264, HEVC, VP9, AV1: Which One Is in Your File
H.264 plays on the widest range of devices and compresses the worst of the four. AV1 compresses the best and costs nothing in licensing, HEVC sits in the middle with a real licensing bill attached, and VP9 splits the difference for free.
HDR Images, and What Happens When They Are Not Tone-Mapped
Convert a real HDR file straight to JPG or PNG and FileFlip's own pipeline clips every highlight to solid white with no warning. Convert a phone's HDR photo the same way and you keep a normal-looking picture, just not a brighter one, because the extra data behind that brightness doesn't survive a plain re-encode.
How a File Converts Without Being Uploaded
FileFlip compiles the same engines a desktop converter uses, FFmpeg, ImageMagick, Pandoc and MuPDF, to WebAssembly and runs them on the page, so your file's bytes never leave the tab.
How a RAW File Becomes a Photo
A RAW file that looks flatter, darker or more washed out than the camera's own screen preview is behaving normally. No browser-based converter applies the manufacturer's tone curve unless it's specifically told to, and FileFlip is no exception.
How Video Compression Works
A video codec keeps a handful of complete pictures and rebuilds everything between them from what changed, so how much a clip shrinks depends on how much of it moves, not on which format you pick.
Indexed Colour and Dithering
A truecolour pixel is three independent numbers; an indexed pixel is one number that points into a shared list of at most 256 colours. That swap saves two-thirds of the file on a photograph and costs almost nothing on flat art, and we measured both.
Interlacing, Combing, and Old Footage
Broadcast and camcorder video often stored half the visible lines twice as often instead of a full frame once, and a comb-toothed frame is what you get when a player draws two of those half-moments on top of each other.
Mono, Stereo, 5.1, and What a Downmix Does
Extra channels only cost you space in an uncompressed file. Feed MP3 or AC-3 a fixed bitrate and mono comes out the exact same size as stereo, byte for byte, because bitrate is a total budget, not a per-channel one.
MP3, AAC, Opus, Vorbis and FLAC
Opus scores highest in blind listening tests at any given bitrate, AAC has the widest hardware decode support of any lossy codec, and MP3 still opens on more devices than either, because its patents expired and it never had to fight for the slot.
OCR, and Why FileFlip Does Not Do It
Reading letters out of a picture is a different job from converting a file, and pretending otherwise produces a document full of confident nonsense.
PDF/A, and Keeping a Document Readable in 2050
PDF/A is a locked-down PDF that bans anything that could stop the file opening the same way after the software that made it is gone, no JavaScript, no encryption, no font that isn't embedded in the file itself.
Progressive vs Baseline JPEG
Baseline and progressive JPEG hold identical pixels, coded in a different order. Baseline fills the picture from the top down as bytes arrive; progressive reveals the whole frame at once, blurry, then sharpens it in later passes.
Resolution, Frame Rate, and File Size
Doubling a video's width quadruples the pixels the encoder has to describe every second, and doubling the frame rate doubles how often it has to describe them. Multiply both together and 4K60 asks for eight times what 1080p30 does.
Sample Rate and Bit Depth
Sample rate sets the highest pitch a recording can hold, and bit depth sets how quiet a sound can get before quantization noise swallows it. Neither one moves your file's size or audible quality anywhere near as much as the bitrate of the codec encoding it.
Text Encodings, and Where the é Went
A file's bytes only turn into letters once something decides which encoding they're in, and CSV and SRT never say. Guess wrong and every accent becomes é or a black diamond, and nothing along the way throws an error to warn you.
What a Conversion Actually Costs You
A conversion copies the bytes, re-encodes them, or throws part of them away, and the format pair decides which, not anything you click. We ran one of each and measured what survived.
What a PDF Really Is
A PDF is a set of drawing instructions plus the fonts to run them, which is why the text is sometimes selectable and sometimes a picture of text.
What Bitrate Controls
Bitrate sets how many bits per second an encoder can spend, and multiplying that by duration gets you roughly the file size before you've encoded anything. Everything else you can set only changes what those bits buy, not how many of them there are.
Which Markdown Are You Actually Writing?
CommonMark, GitHub Flavored Markdown, and Pandoc's own dialect agree on paragraphs, headings, and links, and disagree on almost everything past that, because tables, footnotes, task lists, and strikethrough are all extensions, not universal syntax.
Why Converting the Same File Twice Makes It Worse
A second lossy pass costs you almost nothing when the settings and the file are unchanged. Change the quality, edit the file, or switch formats in between, and that loss is permanent and it stacks on top of the first pass.
Why File Extensions Lie
An extension is a label typed by whoever last saved the file, not a property of the file itself. FileFlip and every real decoder read the bytes instead, so renaming .webp to .jpg changes nothing about what the file actually is.
Why You Can Only Convert From RAW, Never To It
A RAW file is a private dump of exactly what one camera's sensor recorded, not yet a picture, so nothing but that camera can write one and no converter can invent back the color data a JPEG already threw away.
Why Your Operating System Refuses to Decode a File
HEVC and AAC both carry a patent royalty per device, so Windows, some browsers, and plenty of hardware skip the decoder rather than pay it, which is the entire reason the file in front of you won't open.
Lossy vs Lossless Compression
Pick a lossy format when the file is finished and size is what matters, and a lossless one when you will open and re-save it again. Converting a lossy file into a lossless container is the common mistake, and we measured what it costs.
Getting something done#
A thing you are trying to do, and the shortest route to it.
On your device#
What your operating system will and won't open, and what to do when it won't.
When a file won't open#
A file that opens nowhere, an extension that lies, an export that came out wrong.
Aspect Ratio, and Why Your Video Looks Stretched
Old video formats often store a rectangular grid of non-square pixels plus a flag telling a player how wide to stretch them for display, and a squashed picture after converting means a step in that chain read the pixels and dropped the flag.
Video Remuxing vs Transcoding
A conversion finishes in about a second and the file barely changes size when the codec inside already fits the new container. It takes seconds to minutes and the size actually moves when it doesn't, because every frame gets decoded and built back up from scratch.
Why Can't I Select Text in a PDF?
Try to select a word. If nothing highlights, the page is a photograph, and there is no text anywhere in the file to search, copy, or convert.