Frequently Asked Questions
Quick Answers
Find answers to the most common questions about Compresso's privacy-first file processing tools. All conversions happen entirely in your browser.
🔒 Privacy & Security
What is Compresso?
Compresso is a privacy-first file processing toolbox that runs entirely in your browser. We provide tools to convert, compress, and optimize files without ever uploading them to our servers. Your files remain private and secure on your device.
How is my privacy protected?
Your files never leave your device. All conversion and compression happens locally in your browser using WebAssembly technology.
No file uploads to servers
We can't access your files
Is Compresso really free?
Yes! Compresso is completely free to use. All processing happens in your browser, so we don't have server costs for file processing. No hidden fees, no subscriptions, no limits.
Is it safe to process sensitive documents?
Absolutely! Since everything happens locally, your sensitive documents never leave your device. However, always keep backups of important files as a best practice.
⚡ Technical Information
Why is the first conversion slower?
The first time you use a tool, your browser needs to download and initialize the WebAssembly libraries. This is a one-time process that happens in the background.
Good news: Subsequent conversions will be much faster as the libraries are cached in your browser.
What are the file size limits?
These limits ensure optimal performance in your browser and prevent memory issues.
Which browsers are supported?
Compresso works on all modern browsers that support WebAssembly:
Can I use Compresso offline?
After the initial page load, many tools can work offline. However, you'll need an internet connection to initially load the page and download the WebAssembly libraries.
🛠️ File Processing
Why can't I convert my HEIC file?
Make sure your HEIC file is valid and under 50MB. Some corrupted or very old HEIC files may not be supported.
Tip: Try converting with a different tool first to verify the file integrity.
The converted file quality looks poor. How can I improve it?
Most tools offer quality settings. Try adjusting the quality slider to a higher value.
Trade-off: Higher quality means larger file sizes. Find the balance that works for your needs.
Can I convert multiple files at once?
Currently, most tools process one file at a time for optimal performance and reliability.
Coming soon: We're working on batch processing features for multiple file conversions.
🔧 Troubleshooting
The conversion is stuck or taking too long
Try these solutions in order:
Close other browser tabs to free up memory
Try refreshing the page and starting over
Check if your file is within the size limits
Ensure stable internet connection for initial library download
I get an "out of memory" error
This happens with very large files or when your browser is running low on memory:
Quick Fixes
- • Close other browser tabs
- • Try a smaller file
- • Restart your browser
If Problem Persists
- • Use a device with more RAM
- • Try splitting large files
- • Use during off-peak hours
The download doesn't start
Check if your browser is blocking downloads
- • Ensure pop-ups are allowed for compresso.app
- • Try right-clicking the download button and selecting "Save link as"
- • Check your browser's download settings
Something's not working correctly
General troubleshooting steps:
🛡️ Security Verification
How do I know my files are safe?
You can verify our privacy claims yourself:
Technical Verification
- • Monitor network activity during processing
- • All processing happens locally in browser
- • No file uploads to servers
Transparency
- • Open source code available
- • Auditable WebAssembly libraries
- • Clear privacy policy
Can you recover my files if something goes wrong?
No, because we never receive your files.
If something goes wrong during processing, you still have your original files. Only the converted output might be affected. This is actually a security feature - we can't access or recover files because we never had them in the first place.
🖼️ Image Format Questions
Why should I convert HEIC to JPG?
HEIC is iPhone's default photo format since iOS 11, but it's not widely supported outside Apple devices:
- • Works on all devices and platforms
- • Supported by all image editors
- • Easy sharing via email/social media
- • Works with all printers
- • Working only within Apple ecosystem
- • Need smaller file sizes
- • Want highest image quality
- • Archiving original photos
When should I use PNG vs JPG?
Choose based on your image type and requirements:
📸 Use JPG For
- • Photographs with many colors
- • Social media sharing
- • Email attachments
- • Web images (faster loading)
- • When file size matters
🎨 Use PNG For
- • Logos and graphics
- • Screenshots
- • Images with transparent backgrounds
- • Simple illustrations
- • When quality is critical
Rule of thumb: JPG for photos, PNG for graphics and logos.
What are WebP and AVIF? Should I use them?
WebP and AVIF are modern image formats with superior compression:
🌐 WebP (Google)
Advantages:
- • 25-35% smaller than JPG
- • Supports transparency like PNG
- • Good browser support
- • Can include animation
Best For:
- • Modern websites
- • Web applications
- • When file size matters
- • Progressive web apps
🚀 AVIF (Next-Gen)
Advantages:
- • Up to 50% smaller than WebP
- • Excellent quality at low sizes
- • HDR and wide color support
- • Future-proof format
Limitations:
- • Only newest browsers
- • Slower to encode/decode
- • Limited software support
- • Still experimental
Recommendation: Use WebP for modern web projects with JPG fallback. Try AVIF for cutting-edge applications where maximum compression is needed.
Why is my converted image quality poor?
Common Causes of Quality Loss
- • Quality setting too low (especially for JPG)
- • Multiple conversions (JPG → PNG → JPG)
- • Converting to lossy format (PNG → JPG)
- • Original image already heavily compressed
How to Improve Quality
- • Increase quality setting (use 90-95% for JPG)
- • Start with the highest quality original
- • Use lossless formats (PNG, TIFF) for editing
- • Convert to lossy format only once, at the end
Remember: You can't improve quality beyond the original. If your source image is poor quality, the conversion will maintain that quality level.
🎵 Audio Format Questions
What's the difference between MP3, WAV, FLAC, and OGG?
🎵 MP3 (Most Common)
- • Type: Lossy compression
- • Size: Small files
- • Quality: Good (320kbps = excellent)
- • Compatibility: Universal
- • Best for: General music, streaming
🎶 WAV (Professional)
- • Type: Uncompressed/lossless
- • Size: Very large files
- • Quality: Perfect original quality
- • Compatibility: Universal
- • Best for: Audio editing, mastering
🎧 FLAC (Audiophile)
- • Type: Lossless compression
- • Size: Medium (50% smaller than WAV)
- • Quality: Perfect, same as original
- • Compatibility: Good modern support
- • Best for: High-end audio, archiving
🆓 OGG Vorbis (Open Source)
- • Type: Lossy compression
- • Size: Small files
- • Quality: Better than MP3 at same bitrate
- • Compatibility: Good web/gaming support
- • Best for: Web audio, games
Quick recommendation: MP3 for general use, FLAC for quality archiving, WAV for professional editing.
What bitrate should I use for MP3?
MP3 bitrate determines the balance between file size and audio quality:
Acceptable quality • Small files • Good for speech
Good quality • Balanced choice • Most users satisfied
Excellent quality • Indistinguishable from CD • Larger files
Pro tip: Use Variable Bit Rate (VBR) when available - it provides better quality than Constant Bit Rate (CBR) at the same average bitrate.
Will converting MP3 to FLAC improve quality?
No! Converting MP3 to FLAC will NOT improve audio quality.
Here's why this doesn't work:
- • MP3 is lossy: Audio information was permanently removed during MP3 encoding
- • FLAC is lossless: It perfectly preserves whatever you give it, including MP3's quality loss
- • Result: A much larger file with the same MP3 quality
Analogy: It's like making a photocopy of a photocopy - the original blur can't be removed by using better paper.
Better approach: Always start with the highest quality source (WAV, FLAC, or original CD) when creating compressed formats.
🎬 Video Format Questions
Why should I convert MOV to MP4?
MOV is Apple's format, while MP4 is the universal standard:
📱 MOV (Apple)
- • Default on iPhone/iPad recordings
- • High quality, often large files
- • Perfect within Apple ecosystem
- • Limited support on other devices
- • Not ideal for web streaming
🌐 MP4 (Universal)
- • Works on all devices and platforms
- • Optimized for streaming and web
- • Smaller file sizes
- • Supported by all video players
- • Industry standard for distribution
Best practice: Convert iPhone videos to MP4 before sharing, uploading, or long-term storage.
What's the difference between H.264 and H.265?
These are video codecs (compression methods) used inside MP4 containers:
📼 H.264 (AVC)
Pros:
- • Universal compatibility
- • Hardware acceleration on all devices
- • Fast encoding/decoding
- • Proven reliability
Best for: General use, older devices, streaming
🎬 H.265 (HEVC)
Pros:
- • 50% better compression than H.264
- • Excellent for 4K video
- • Better quality at same file size
- • Future-proof technology
Cons: Limited older device support
Recommendation: Use H.264 for maximum compatibility, H.265 for 4K content or when file size is critical.
Why is video processing so slow?
Why Video Takes Longer
- • Videos contain thousands of images (frames)
- • Each frame must be processed individually
- • Audio track also needs processing
- • Video encoding is computationally intensive
- • Browser processing has limitations vs dedicated software
Ways to Speed Up Processing
- • Use smaller video files (under 100MB)
- • Close other browser tabs and applications
- • Use Chrome or Edge for best performance
- • Consider lowering output quality/resolution
- • Be patient - it's doing complex work!
Typical times: A 10MB video might take 1-3 minutes to convert, while a 100MB video could take 10-30 minutes depending on your device.
📄 Document Format Questions
When should I convert Word/Excel to PDF?
Convert to PDF when you want to:
🔒 Finalize & Protect
- • Prevent accidental edits
- • Lock formatting in place
- • Create official documents
- • Add password protection
- • Digital signatures
🌐 Share & Distribute
- • Ensure consistent appearance
- • Universal compatibility
- • Professional presentation
- • Email attachments
- • Print-ready documents
Keep both versions: Keep the original Word/Excel file for future editing, and create a PDF for sharing and archival.
Can I convert PDF back to Word for editing?
Yes, but with limitations! PDF to Word conversion works best with text-heavy documents.
✅ Works Well For
- • Simple text documents
- • Basic formatting
- • Documents with standard fonts
- • Clean, well-structured PDFs
❌ Challenging For
- • Complex layouts
- • Tables and charts
- • Scanned PDFs
- • Multiple columns
- • Heavy graphics/images
Tip: Always review the converted document carefully and expect to do some formatting cleanup.
How do I create a PDF from multiple images?
Use our image-to-PDF converter to combine multiple images into a single PDF document:
📋 Step-by-Step Process
- Go to any image-to-PDF converter tool
- Select multiple images at once (Ctrl+click or Cmd+click)
- Images will be processed in the order selected
- Each image becomes one page in the PDF
- Download your combined PDF
💡 Pro Tips
- • Name your images with numbers (001, 002, 003) for correct order
- • Use consistent image sizes for best results
- • JPG images are processed faster than PNG
- • Consider optimizing large images first to reduce PDF size
🎯 Perfect For
- • Scanning documents with your phone
- • Creating photo albums
- • Portfolio presentations
- • Combining screenshots into one file
💡 Pro Tip: Use Ctrl+F to Search
Use your browser's search function (Ctrl+F or Cmd+F) to quickly find specific topics within this FAQ.
Still have questions?
If you can't find the answer you're looking for, we're here to help. Check out our documentation or learn more about our privacy practices.