Converting (the file format used by Scratch 3.0 ) is a common task for developers looking to manually edit project files. Because an file is essentially a renamed archive containing a project.json
file and various assets (costumes and sounds), you can easily move between these formats. Guide: Converting ZIP to SB3 (Extra Quality)
"Extra Quality" in this context typically refers to ensuring your assets (images and audio) remain uncompressed and correctly linked during the re-zipping process to prevent data loss or project corruption. 1. Prepare Your Assets : Ensure your root folder contains the project.json
file and all associated media files (typically named as hashes like a1b2c3...svg
: Do not rename the assets manually unless you also update their corresponding entries in the project.json 2. Create the ZIP Archive : Select only the files your project folder (the JSON and media files). Do
zip the parent folder itself, as Scratch will fail to find the project.json at the root. Compression Method : For "Extra Quality," use compression levels in tools like
. Avoid "Ultra" compression as it can sometimes lead to extraction errors in web-based environments. Dropbox.com 3. Rename to .sb3 Once you have your project.zip file, right-click it and select Change the extension from zip to sb3 extra quality
If you don't see the extension, enable "File name extensions" in your operating system's view settings. 4. Verify in Scratch Scratch Editor Navigate to File > Load from your computer and select your new
Check that all high-quality vector images or high-bitrate sounds are playing correctly without distortion. Advanced "Extra Quality" Tips What a ZIP File Is and How They Work - Dropbox.com
In the context of Scratch 3.0, ZIP and SB3 files are essentially the same thing . An .sb3 file is simply a ZIP archive that has been renamed with a different extension . "Extra quality" in this conversion usually refers to manually optimizing the assets (images and sounds) inside the ZIP before renaming it back to SB3 to ensure the project remains high-quality while staying within Scratch's file size limits . How the Conversion Works
Because an SB3 file is a renamed ZIP, you can move between the two formats freely to edit project internals .
SB3 to ZIP: Change the file extension from .sb3 to .zip . You can then extract it to see a project.json file and various asset files (like .svg, .png, or .wav) .
ZIP to SB3: After making changes, select all files inside the project folder (not the folder itself), compress them into a new ZIP, and rename that ZIP to .sb3 . Achieving "Extra Quality" and Optimization Converting (the file format used by Scratch 3
When users talk about "extra quality" or high-performance conversion, they are typically referring to these manual optimizations within the ZIP structure:
Audio Compression: Replace large .wav files with high-quality, lower-bitrate .mp3 files to save space without a noticeable drop in sound quality .
Image Optimization: While Scratch often converts images, you can manually inject high-resolution .svg (vector) or optimized .png files directly into the ZIP archive .
Lossless Compression: Using tools like 7-Zip to compress the final ZIP can sometimes result in a smaller file size than the standard Scratch "Save to computer" function, though the savings are often minor since ZIP is already a lossless format . How can I directly modify a .sb3 file? - Discuss Scratch
Replace the if __name__ == "__main__" block with:
if __name__ == "__main__":
import sys
if len(sys.argv) < 2:
print("Usage: python convert_to_sb3.py input.zip [output.sb3]")
sys.exit(1)
input_file = sys.argv[1]
output_file = sys.argv[2] if len(sys.argv) > 2 else None
zip_to_sb3_extra_quality(input_file, output_file)
Then:
python convert_to_sb3.py my_scratch_project.zip my_optimized.sb3
The Scratch community is pushing for a formal "Lossless SB3" specification. Proposed features include:
Until then, following the ZIP to SB3 extra quality guidelines in this article ensures your projects remain studio-grade, whether you're sharing on the Scratch website, embedding in TurboWarp, or archiving for future generations.
Corrupted project.json is the #1 cause of failed imports. Use a JSON validator. Extra quality means checking:
assets folder.Pro tip: Open project.json in VS Code or Notepad++ to detect hidden BOM characters that break Scratch’s parser.
This is the secret to extra quality. Most ZIP tools use DEFLATE compression (level 6). But for SB3, you need:
How to do it in 7-Zip:
zipFastest (this prevents over-compressing PNGs)Deflate32 KB or less (Scratch’s built-in ZIP uses small dictionaries)Why “Fastest” = Extra Quality?
Because slower compression (Ultra) re-encodes PNG chunks and can alter audio headers. For SB3, faster compression preserves binary integrity.