Published Mar 19, 20268 min read
By ChangeThisFile Team
Quick Answer
The right file format depends on the use case: JPG for email photos, WebP/AVIF for web images, PDF for documents, MP4 H.264 for shareable video, FLAC for audio archival, and CSV/JSON for data exchange. This guide provides decision matrices for every combination of use case and media type.
You have a file. You need to send it somewhere. What format should it be in? The answer depends on two things: what the file contains (image, video, audio, document, data) and where it's going (email, web, print, archive, social media, professional handoff). Get the combination right and everything works smoothly. Get it wrong and you're dealing with rejected uploads, degraded quality, or files the recipient can't open.
This guide provides a definitive decision matrix: rows are use cases, columns are media types, and each cell contains the recommended format with a one-line rationale. Bookmark it. The next time you're choosing a format, the answer is in one of these tables.
Image Format Decision Matrix
Use Case
Best Format
Why
Convert From
Email attachment
JPG (quality 80-85)
Universal support, small file size, under email limits
Is it a photo? → JPG for sharing, WebP/AVIF for web, TIFF for print/archival
Does it need transparency? → PNG (raster), SVG (vector), WebP, or AVIF
Is it a logo/icon/diagram? → SVG (scalable vector) or PNG (raster with flat colors)
Is it a screenshot? → PNG (preserves text sharpness)
Is it for web delivery? → AVIF → WebP → JPG (fallback chain)
Is it for archival? → TIFF or PNG (lossless, open spec)
Video: Which Format?
Does it need to play everywhere? → MP4 with H.264 + AAC
Is file size the priority? → MP4 with AV1 (modern devices) or H.265 (Apple devices)
Is it for editing? → ProRes (macOS) or DNxHR (Windows) — never H.264
Is it for archival? → MKV with FFV1 (lossless) or H.264 CRF 18 (practical)
Is it a short loop/animation? → MP4 or WebM, never GIF (10x smaller)
Document: Which Format?
Does the recipient need to edit it? → DOCX (or ODF for open-format preference)
Is it view-only? → PDF
Is it for long-term archival? → PDF/A
Is it for a developer audience? → Markdown
Does only the content matter, not formatting? → TXT (UTF-8)
Format selection isn't about finding the objectively "best" format — it's about matching the format to the use case. AVIF is technically superior to JPG, but if you're emailing a photo to your grandmother, JPG is the right choice because it opens on her 2018 iPad without thinking about it. MKV with FFV1 is superior for archival, but if you're sharing a clip on Discord, MP4 H.264 is what works.
Use these decision matrices as a reference. When you know the format, use ChangeThisFile to get there. The conversion is the easy part — choosing the right destination format is where the thinking happens.
Key Takeaways
JPG is the universal safe choice for photos; WebP/AVIF are better for web but require fallbacks
MP4 with H.264 is the only video format guaranteed to play everywhere without codec installation
PDF is the right format for any document that doesn't need to be edited by the recipient
CSV is the universal data exchange format; Parquet is the modern choice for large datasets
ZIP is the only archive format every OS can extract without extra software
Format choice depends on destination (email, web, print) as much as content type (image, video, audio)
When in doubt: JPG for images, MP4 for video, MP3 for audio, PDF for documents, ZIP for archives
Frequently Asked Questions
What's the single most universally compatible image format?
JPEG. It's supported by every browser, every phone, every email client, every image viewer, every printer, and every operating system released in the last 30 years. No other image format comes close to JPEG's universal compatibility. It's lossy, so it's not ideal for everything, but if compatibility is the only consideration, JPEG wins.
Should I use WebP or AVIF for my website?
Both are good choices. AVIF provides 20-30% better compression than WebP but is slower to encode and has slightly less browser support (Safari 16.4+, added 2023). WebP has near-universal support since 2020. The pragmatic approach: use AVIF with WebP as first fallback and JPEG as second fallback in an HTML picture element. If you want simplicity, WebP alone covers 97%+ of browsers.
Why do some websites still use PNG instead of WebP?
Three reasons: (1) PNG is lossless by default — for screenshots, diagrams, and text-heavy images, PNG's sharpness matters. (2) Tool ecosystem — many CMS platforms, image editors, and workflows default to PNG. (3) Inertia — WebP has only been universally supported since 2020, and many websites haven't updated their image pipelines. For new content, WebP is the better choice for web delivery in almost all cases.
What format should I use for a video that needs to work on very old devices?
MP4 container with H.264 Baseline profile video and AAC-LC audio. The Baseline profile (versus Main or High profile) ensures compatibility with the oldest H.264 decoders, including 2010-era smartphones and TVs. Resolution should be 720p or below for maximum compatibility. This combination works on virtually every device manufactured after 2008.
Is there a single format that works for everything?
No, and there never will be. A format optimized for photographic compression (JPEG) is terrible for text documents. A format optimized for archival (TIFF) is wasteful for web delivery. A format optimized for editing (PSD) is unreadable outside specialized software. The closest to universal is PDF for documents and MP4 for media, but even these have limitations.
What audio format should I use for voice recordings?
Opus at 48-64 kbps for the best quality per file size. Opus was specifically designed to handle speech and music adaptively. If compatibility with older devices matters, AAC at 64-96 kbps (M4A container) is the safe choice. For archival of important recordings, WAV or FLAC to preserve everything. MP3 at 128 kbps is the fallback for maximum compatibility.
Why does every platform recommend MP4 for video upload?
MP4 with H.264 has hardware decoders in every modern device (phones, tablets, smart TVs, streaming boxes), making it cheap and fast to process. Platforms like YouTube, Instagram, and TikTok re-encode everything anyway, but starting from MP4 H.264 means the upload is smaller, the processing is faster, and there are fewer codec compatibility issues during transcoding.
Should I send CSV or XLSX when sharing data?
CSV if the recipient just needs the data (importing into a database, loading into Python, feeding into another tool). XLSX if the recipient needs to view it as a formatted spreadsheet with headers, column widths, and human-readable layout. CSV is more portable and tool-agnostic. XLSX is more human-friendly. When in doubt, send both.