Raw, uncompressed video is enormous — far too large to stream practically. Compression is what makes streaming possible at all.
The basic idea
Video compression removes redundant information. Two consecutive frames in a video are often very similar, so instead of storing each frame in full, compression stores only what changed between them.
Lossy vs. lossless compression
Streaming video uses lossy compression, discarding some detail the human eye is less likely to notice, in exchange for dramatically smaller file sizes. This is different from lossless compression (like a ZIP file), which preserves every detail exactly.
Codecs do the heavy lifting
The specific compression method is handled by a codec — see our guides to H.264 vs H.265 and AV1 for the most common ones used in streaming today.
Why this matters practically
More efficient compression means better quality at the same file size, or the same quality using less bandwidth — directly affecting how smoothly a stream plays on your connection.