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The ideas under every file, running live.

Thirteen concepts explained, and together they cover almost everything a converter does: bytes, pixels, sample rates, codecs, containers, bitrate and the two kinds of compression. Each one below comes with a small working demonstration computed in your browser, not a diagram. Each also links to the page on this site where you can see it at full depth on your own files.

that headline, measured just now

41 bytes41 characters, stored as UTF-8 textdigital file

43 bytesafter DEFLATE: 5% larger: too short and varied to compresscompression

666 × 132device pixels it covers on your screen (1× density)resolution

343.4 KBraw RGBA memory to paint those pixelspixel

pick a concept · outlined ones connect to it

01 · Building blocks

descriptionDigital fileinfoMetadata

02 · Pictures

grid_onPixelaspect_ratioResolutionimageImage format

03 · Sound & motion

graphic_eqDigital audiomovieDigital videomemoryCodecinventory_2ContainerspeedBitrate

04 · Making it smaller

compressCompressionverifiedLossless compressiontuneLossy compression

compressmaking it smaller · 11 of 13Compression

Storing the same information in fewer bytes by finding patterns: repeated strings, predictable values, common symbols.

sciencetry it

×1×10×100

original450 bytes

DEFLATE (raw)52 bytes · 12%

gzip (adds 18-byte header + trailer)70 bytes

Real CompressionStream output. Repeat the text ×10 or ×100: the original grows 10-100×, the compressed copy barely grows, because DEFLATE stores each repeat as a short back-reference.

connects to

Lossless compressionarrow_forwardLossy compressionarrow_forward

see it in depthZIPInside a real ZIP, entry by entry see it in depthArchive ToolsPer-file vs solid compression

Building blocks

What a file is, and what is written inside it besides the content.

descriptionDigital file

A named sequence of bytes. Nothing in the bytes says "photo" or "song" except conventions: a signature at the start and a structure that software agrees on.The name .jpg is a hint. The bytes FF D8 FF are what make it a JPEG.

scienceTry it Identify any file from its bytesarrow_forward

infoMetadata

Data about the data: dates, camera, GPS position, author, software, editing time. It travels inside the file and is easy to forget.A phone photo can carry the exact spot it was taken. A Word file can name every author who edited it.

scienceTry it Every EXIF tag, incl. GPSarrow_forward

Pictures

How images become grids of numbers, and how those grids are stored.

grid_onPixel

One sample of colour in a grid. On most screens it is three numbers, red, green and blue, from 0 to 255.#4f46e5 is just red 79, green 70, blue 229: three bytes.

scienceTry it Click a pixel to read its bytes; your screen measuredarrow_forward

aspect_ratioResolution

How many pixels wide and tall. More pixels hold more detail, and cost more bytes before compression.3840 × 2160 (4K) is 8.3 million pixels: four times 1080p.

scienceTry it Pixels per inch and viewing distancearrow_forward

imageImage format

The rules for storing a pixel grid: which compression, whether transparency or animation fit, and what metadata goes where.The same picture as PNG, JPEG and WebP can differ several-fold in size.

scienceTry it Ten formats ranked and tested; real header bytesarrow_forward

Sound & motion

How audio and video become data, how they are squeezed and how they are packed.

graphic_eqDigital audio

Sound measured thousands of times a second. The sample rate sets the highest frequency kept (half the rate), and the bit depth sets how quiet the noise floor is.CD audio: 44,100 samples a second, 16 bits, two channels.

scienceTry it Hear aliasing; samples as WAV bytesarrow_forward

movieDigital video

A run of still frames shown fast enough to look like motion, usually with one or more audio tracks alongside.At 30 fps, one minute of video is 1,800 pictures.

scienceTry it Real H.264 frame sizes, keyframes, 4:2:0arrow_forward

memoryCodec

The method that compresses video or audio and decodes it again. It decides quality per byte; the file type does not.H.264, HEVC and AV1 are codecs. All three can live inside an .mp4.

scienceTry it 90 frames through a real encoderarrow_forward

inventory_2Container

The file structure that holds compressed tracks together, with timing, track names, chapters and an index for seeking.MP4, MKV and WebM are containers. Remuxing between them can be lossless.

scienceTry it EBML elements and Cuesarrow_forward

speedBitrate

Bits spent per second. Duration × bitrate is the file size, which is why size targets turn into bitrate targets.128 kbit/s for 3 minutes is 2.9 MB of audio.

scienceTry it Constant vs variable, measured in your browserarrow_forward

Making it smaller

The two ways to make data smaller, and what each one costs.

compressCompression

Storing the same information in fewer bytes by finding patterns: repeated strings, predictable values, common symbols.Text repeated 100 times compresses to little more than one copy.

scienceTry it Inside a real ZIP, entry by entryarrow_forward

verifiedLossless compression

Compression that rebuilds the original exactly, bit for bit. It only removes redundancy, so how much it saves depends on the content.PNG, FLAC and ZIP decompress to identical bytes, checkable with a hash.

scienceTry it Round trip with SHA-256, PNG filters, FLAC predictorsarrow_forward

tuneLossy compression

Compression that throws away detail it judges you won’t notice, in exchange for much smaller files. What’s removed never comes back.JPEG, MP3 and H.264 all quantise: they round off fine detail.

scienceTry it 30 re-saves and the sound Opus removedarrow_forward

From ideas to your own files

fingerprintFormats explainedDrop any file and see what it really is from its bytes, then open one of 34 format reference pages with a byte-level inspector.photo.jpg → actually PNG compare_arrowsComparisonsAny two of 30 formats side by side, what each conversion direction loses, and a measured size race for image pairs..jpg vs .webp → 3 rows differ routeGuidesPick what you have and what you need; each pair shows what survives and where to convert it..heic → .jpg

Deep dives

compressCompressionEntropy, Huffman, LZ77 and Deflate measured on your own text.paletteColour spacesOne colour in nine spaces, a live gamut map and three ways to blend.stairsBit depthBanding in skies and hiss in quiet sound, at any depth you choose.movieCodecsHow video and audio codecs trade size for quality.inventory_2ContainersThe box around the data, laid out block by block from real bytes.sellMetadataWhat a file says about who made it, where and when, and how to remove it.translateText encodingWhy "Café" turns into "CafÃ©", byte by byte, and how to tell which encoding a file uses.straightenResolution & DPIPixels set the detail; the dpi label only sets the print size. How big an image can print.frame_inspectFile typesExtensions versus magic bytes: what a file really is, and who trusts the name.