A 30-second video clip on your phone can easily be larger than a folder containing dozens of documents, PDFs, and spreadsheets combined. It sounds disproportionate until you think about what a video file actually is — and once that clicks, the file size makes a lot more sense.
Video is essentially a rapid sequence of individual frames — often 30 or more per second — each one comparable to a full photo. A 30-second clip at that rate contains close to a thousand individual images stitched together with audio, which is exactly why the file size adds up so quickly compared to a single static photo or a text document.
Recording in higher resolution or a higher frame rate — increasingly common defaults on newer phones — captures more visual data per frame and more frames per second, both of which directly increase file size. A video recorded at a phone's highest quality setting can be dramatically larger than the same clip recorded at a more modest setting, often without much visible difference at normal viewing sizes.
The audio track riding alongside the video adds its own data on top of the visual frames — not usually the dominant factor in file size, but a real contributor, especially for longer clips where the audio track accumulates over time right alongside the video data.
Video compression takes advantage of the fact that most frames are very similar to the frame right before them — rather than storing every frame in full detail, it can store the differences between frames, which is far more efficient than treating each frame as a completely separate image. This is part of why dedicated video compression can shrink file size significantly without an equally dramatic visible quality drop.
If a video is too large to send easily over WhatsApp or email, compressing it before sending — rather than trying to send the original high-resolution recording — usually solves the problem without a noticeable quality loss for typical viewing on a phone screen.
Video files are simply a different category of "big" compared to documents or even photos — understanding why makes the file sizes feel less surprising, and makes compression feel like the obvious first step rather than a last resort.