Know When Not to Compress: Save Time by Skipping the Unshrinkable
Not every file benefits from compression—and trying can waste time, battery, and even make files larger. Learn how to quickly spot already-compressed data, set smart rules for mixed folders, and choose workflows that make your archives smaller without extra effort.
The hidden cost of compressing the uncompressible
Many everyday file types are already compressed. Photos (JPEG, HEIC), videos (MP4, MKV), audio (MP3, AAC), and many document formats (DOCX, PPTX, XLSX, EPUB) contain their own compression inside. Running them through a compressor again often yields no savings—or worse, increases size because the compressor has to store its own dictionary and metadata on top of data that’s already entropy-dense. There are also practical costs: extra CPU time, higher energy use on laptops and phones, and slower archiving pipelines. If your goal is a quick upload or a portable bundle, blindly compressing everything can be the slowest path to the same result. Recognizing which files won’t shrink lets you choose a faster “store-only” approach while still keeping a single archive for distribution.
Fast ways to gauge compressibility
File extensions are a helpful first pass: JPEG, PNG, MP4, MP3, PDF, and modern office documents usually compress poorly. Plain text, CSV, JSON, logs, source code, and raw bitmaps compress very well. But extensions can mislead—some PDFs are lightweight wrappers around images, while others contain uncompressed vector data. A quick, low-cost test is to compress a tiny sample (for example, the first 256 KB of a file) and compare before/after size. If the test shows less than a few percent gain, treat the file as non-compressible. Another tell is repetition and structure: long runs of zeros, repeated headers, or predictable text patterns typically shrink, while noisy, high-entropy data will not. With a little practice, you’ll develop an eye for which folders are worth compressing and which ones are just better stored.
Smarter workflows for mixed-content folders
Most real-world folders mix text, images, media, and application bundles. Instead of a one-size-fits-all setting, split your strategy by content. Use “store” (no compression) for images, videos, audio, and any files that are themselves archives or disk images. Apply compression to text-heavy materials like CSVs, logs, configs, source code, and JSON. If you want a single deliverable, you can still build one archive that mixes methods—good tools let you store certain files while compressing others. For especially diverse projects, consider two-stage packaging: group similar files into sub-archives by type (for example, one archive for media stored as-is, another for text compressed aggressively), then bundle those sub-archives together. This keeps compression effective without wasting time on data that won’t budge.
When re-compression actually helps
Sometimes shrinking starts before archiving. Large bitmap screenshots saved as BMP or TIFF can be converted to PNG or lossless WebP and then archived; massive CSVs can be cleaned by removing redundant columns or normalizing repeated values; vector-heavy PDFs often compress more if you downsample oversized images inside them. For scanned PDFs that are just images, running OCR can reduce size by replacing image-heavy pages with text and simpler vector elements. These are content-aware steps: the archive doesn’t do the heavy lifting, but your pre-processing does. The net result is a smaller, more useful archive that still opens easily across systems.