File compression explained: images vs video vs PDF

Compression means storing the same content using fewer bytes. How that works depends a lot on the file type. Understanding the basics helps you pick the right settings and know what to expect.

Lossy vs lossless

Lossless compression keeps every detail and just stores it more efficiently, like zipping a document. Lossy compression discards data the human eye or ear is unlikely to notice, which shrinks files far more. Most media uses lossy compression because the savings are huge and the quality cost is small.

Images

Image compression reduces size by simplifying detail and using efficient formats. Choosing a modern format like WebP or AVIF, picking a sensible quality level around 70 to 80, and resizing to the dimensions actually displayed are the three biggest levers.

Video

Video is a sequence of frames, so it compresses by storing only what changes between frames and by using efficient codecs like H.264 or H.265. A CRF setting controls quality, and lowering resolution further reduces size when full resolution is not needed.

PDF and presentations

PDFs and PowerPoint files are mostly containers. Their text is tiny; the weight comes from embedded images. Compressing a PDF or a PPTX therefore means re-compressing those embedded images, which is why the layout stays identical while the file shrinks.

One tool for all of them

Because the principles differ by file type, the right engine differs too. CompressEasy Desktop applies the correct method to each file automatically, so you can compress images, video, PDF, and presentations in one place, offline.