format-support.csv

format,can_decode,can_encode,decode_mechanism,encode_mechanism,feature_detect,notes
PNG,yes,yes,"Browser image decode through HTMLImageElement (loadRasterImage, png.loadPngImage), drawn onto a 2D canvas","canvas.toBlob('image/png') (canvasToPngBlob, png.rgbaToPngBlob). png.encodeAnimatedPng also writes a single-frame PNG through UPNG (pure JS) when you pass one frame",none needed (Canvas 2D),"No WebAssembly and no ffmpeg on this path. png.isPngFile() classifies the file"
APNG,yes,yes,"UPNG.decode plus UPNG.toRGBA8 (pure JS, @pdf-lib/upng) through png.decodeAnimatedPng","UPNG.encode (pure JS) through png.encodeAnimatedPng; the loop count is patched into the acTL chunk by png.patchApngLoopCount",none needed (pure JS),"The colorCount argument drives palette quantization, so this encoder is lossy by design. Frames go in and out as RGBA Uint8Array"
JPEG,yes,yes,"WebCodecs ImageDecoder first, with a pure-JS JPEG decoder (from the inlined @cross/image) as the fallback: jpg.decodeJpegLikeSource asks for runtimeDecoding 'prefer'. Other paths simply decode through HTMLImageElement","MozJPEG WebAssembly (@jsquash/jpeg) through jpg.encodeJpegBlobFromImageData, which exposes progressive and chroma-subsampling flags. canvasToBlob(canvas, 'image/jpeg', quality) is the plain-canvas alternative","none exported (the MozJPEG path needs WebAssembly, the canvas path needs nothing)","This is the only place the library ships a real codec of its own. jpg.inspectJpegStructure reads component count, progressive flag and Adobe transform straight from the bytes; EXIF is read with exifr"
HEIC / HEIF,browser-dependent,no,"WebCodecs ImageDecoder with type image/heic, through jpg.decodeJpegLikeSource. The inlined @cross/image has no pure-JS HEIC fallback, so on a runtime whose ImageDecoder cannot handle image/heic the call throws",not supported,"none exported for HEIC. jpg.isHeicFile() only classifies the file, it does not test the runtime","Accepted extensions and types: .heic, .heif, image/heic, image/heif, image/heic-sequence. Decoded HEIC is re-encoded through the JPEG, PNG or WebP paths"
WebP (still),yes,yes,"Browser image decode through HTMLImageElement (webp.renderStillWebpImageData). webp.readWebpMetadataFromBytes parses the RIFF chunks in pure JS without decoding anything","OffscreenCanvas.convertToBlob({ type: 'image/webp' }) inside the inlined @cross/image (webp.recompressStillWebp, webp.optimizeWebp), with a pure-JS VP8L lossless encoder as the fallback when OffscreenCanvas is missing. canvasToBlob(canvas, 'image/webp', quality) is the plain-canvas alternative","none exported for still WebP","Two honest caveats in the encode path: the lossless flag only reaches the pure-JS VP8L fallback (the OffscreenCanvas branch passes quality only), and that branch does not check the returned blob type, unlike the AVIF branch"
WebP (animated),browser-dependent,yes,"WebCodecs ImageDecoder, one frame at a time (webp.decodeAnimatedWebpFrames); each VideoFrame is drawn to a canvas and exported as PNG","ffmpeg.wasm with the libwebp_anim encoder, fed a PNG frame sequence and a concat manifest (webp.encodeAnimatedWebp)","webp.canDecodeAnimatedWebpInBrowser() to decode (checks ImageDecoder), gif.canUseFfmpegInBrowser() to encode","Frame count and per-frame delays come from the pure-JS RIFF parse of the ANIM and ANMF chunks, not from the decoder"
AVIF,browser-dependent,browser-dependent,"WebCodecs ImageDecoder with type image/avif, inside the inlined @cross/image (avif.readAvifSource). No WebAssembly AVIF decoder is shipped","OffscreenCanvas.convertToBlob({ type: 'image/avif', quality }) inside the inlined @cross/image. The browser's own AVIF encoder does the work; if the returned blob is not image/avif the call throws instead of handing back a PNG","avif.canProcessAvifInBrowser() (checks window.ImageDecoder and window.OffscreenCanvas). avif.assertAvifRuntime() throws the same check","Still images only, there is no animated-AVIF path. Quality is 1 to 100; the presets balanced/smaller/aggressive map to 70/56/42"
GIF (animated),yes,yes,"ffmpeg.wasm decodes the frames to PNG (gif.extractGifFrames, gif.extractGifPreviewFrame). gif.readGifMetadata reads size, frame count, delays, loop count and transparency from the bytes in pure JS. An HTMLImageElement decodes the first frame only","ffmpeg.wasm with a palettegen and paletteuse filter graph (gif.encodePngSequenceToGif, and the transforms optimizeGif, resizeGif, cropGif, trimGif, changeGifSpeed, reverseGif, splitGif)","gif.canUseFfmpegInBrowser() (checks window, Worker and document)","ffmpeg-core.js, ffmpeg-core.wasm and ffmpeg-core.worker.js are fetched from the jsDelivr CDN on first use and cached for the tab; the image itself is never part of that request"
GIF (single frame),no,yes,"Not in this module. Decode a GIF with gif.extractGifFrames or an HTMLImageElement","Dependency-free pure-JS GIF89a writer (gifEncoder.encodeGif): median-cut quantization to at most 256 colours, then variable-width LZW. No ffmpeg, no WebAssembly, no network",none needed (pure JS),"Writes fully opaque frames: GIF only carries 1-bit transparency, so flatten alpha onto a background first. One frame per call"
ICO,no,yes,not supported,"Pure-JS ICONDIR and ICONDIRENTRY container packing canvas-encoded PNG payloads (ico.buildIcoBlob, ico.encodeIco, ico.renderPngAtSize, and png.createIcoBuffer)",none needed (Canvas 2D),"ico.ICO_SIZE_OPTIONS is 16, 32, 48, 64, 128, 256. ico.verifyIcoHeader re-reads the container before download. Sizes of 256 are written as 0 per the ICO spec"
BMP,yes,no,"Browser image decode through HTMLImageElement: image/bmp is in rasterImageMimeTypes and isRasterImageFile() accepts .bmp",not supported,none needed (Canvas 2D),"There is no BMP module. BMP is only an accepted input to the shared canvas helpers, and it leaves as PNG, JPEG, WebP or AVIF"
MP4,yes,yes,"ffmpeg.wasm reads mp4, mov, m4v, webm, avi and mpeg input (gif.convertVideoToGif, webp.convertVideoToWebp, gif.extractVideoClipFramesAsPng)","ffmpeg.wasm from a PNG frame sequence (gif.convertGifToMp4, webp.convertWebpToMp4): yuv420p, crf 23, faststart, no audio track",gif.canUseFfmpegInBrowser(),"Video, listed because the GIF and animated-WebP paths convert to and from it. The source sets no -c:v, so ffmpeg's default encoder for the mp4 container is used"
JPEG XL,no,no,not implemented,not implemented,"none: the library has no JPEG XL path","Listed because it is the question people ask next. There is no JXL codec bundled, no canvas type and no WebCodecs type for it anywhere in src/"