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Need help?How to Re-save an SWF File Online
- Upload Your SWF File: Drag and drop or click "+ Add Files" to load one or more .swf files (FWS, CWS, or ZWS signature — all three are accepted). Batch processing is supported.
- Pick a Quality Preset: Default is Very High (Recommended). Choose a lower preset to shrink long animations, or switch File Compression to Specific file size for a megabyte target, or Constant Bitrate / Constant Quality when you need predictable streaming behaviour.
- Resize and Trim (Optional): Use Preset Resolutions to drop a 1080p movie to 768p or 480p, type custom Width x Height (aspect ratio locked), scale by Resolution Percentage, or set a Trim Time Range to keep only the section you need.
- Convert and Download: Click "Convert". Files process on our servers and are auto-deleted within hours — no sign-up, no watermark, no Flash Player install required.
Why Re-save an SWF File?
SWF (Small Web Format / ShockWave Flash) was Adobe's vector animation container, and although Flash Player reached end-of-life on December 31, 2020, billions of .swf files survive in archives, school CDs, e-learning courseware, and game preservation repositories. Re-saving an SWF to SWF re-encodes the video stream inside it and writes a new .swf around that video. Vector shapes and ActionScript are not carried over, so a SWF that is only a vector animation or a game can't be re-saved here — we tell you right after upload. To keep one of those playable, leave it as it is and open it in Ruffle.
- Shrink a CWS or FWS file to ZWS (LZMA). The SWF spec defines three signatures: FWS (uncompressed, any version), CWS (zlib/DEFLATE, SWF 6+), and ZWS (LZMA, SWF 13+). Re-saving to a smaller compression typically reduces file size by 10-40% versus zlib, which matters when serving Ruffle bundles over slow connections.
- Re-pack an SWF for slow CPUs. Older netbooks, Raspberry Pi boards, and low-end Android tablets running Ruffle decompress LZMA significantly slower than zlib. Re-saving a ZWS-LZMA file to CWS-zlib trades ~15% larger file size for faster startup on weak hardware.
- Resize a high-resolution Flash video for embedding. Re-saving with a smaller resolution and a lower quality preset can cut the file by half or more.
- Trim courseware to a short loop. Educational SWFs frequently contain a 10-minute lesson when you only need a 20-second loop. Use Trim Time Range to keep the section that still matters and discard the rest.
SWF Compression Signatures Compared
| Signature | Algorithm | SWF version | Best for | Trade-off |
|---|---|---|---|---|
| FWS | None (uncompressed) | Any (1+) | Editing, hex-patching, debugging | Largest file size; full payload visible |
| CWS | zlib / DEFLATE | 6 and later | Widest playback compatibility | Medium size; fast to decompress |
| ZWS | LZMA | 13 and later | Smallest distribution size | Slower decompress on weak CPUs |
Quality Preset Quick Guide
| Preset | Visual quality | Typical size vs source | When to use |
|---|---|---|---|
| Very High (Recommended) | Visually lossless | 90-110% | Default; archival re-save |
| High | Subtle softening on gradients | 70-85% | E-learning, web embed |
| Medium | Noticeable on photo bitmaps inside SWF | 45-65% | Bandwidth-constrained hosting |
| Low | Soft on edges, banding in fades | 25-40% | Preview thumbnails, mobile previews |
Frequently Asked Questions
Why re-save an SWF instead of converting it to MP4 or GIF?
Only when a tool down the line needs a .swf file. Re-saving here keeps the video inside the SWF, not its vector shapes or ActionScript, so an interactive SWF (quiz, game, button-driven banner) should stay exactly as it is and play through Ruffle. For sharing the video, SWF to MP4 plays everywhere.
Will my SWF play in browsers in 2026?
Not natively. Chrome, Firefox, Edge, and Safari all removed the Flash Player plugin in January 2021 and Adobe stopped shipping Player updates on December 31, 2020. You need an emulator — Ruffle is the most active project and now implements roughly 90% of the ActionScript 3 language and ~77% of the AS3 API, so most AS1/AS2 SWFs and a growing share of AS3 SWFs play correctly. Lightspark is the alternative for niche AS3 cases.
Does Ruffle care which compression signature my SWF uses?
Ruffle reads FWS, CWS, and ZWS interchangeably. The visible difference is startup time on low-power devices: ZWS-LZMA files take longer to decompress than CWS-zlib of the same logical size. If your audience uses Raspberry Pi or older Chromebooks, re-saving ZWS to CWS measurably improves first-frame latency.
Will re-saving an SWF break ActionScript or interactive content?
Yes — re-saving keeps only the video (and sound) inside the SWF, so ActionScript, buttons and vector shapes are not in the new file. An interactive SWF with no video inside can't be re-saved at all; we tell you right after upload. Keep the original and play it in Ruffle.
What is the difference between SWF version 6, 9, and 13?
SWF version is stamped in byte 4 of the file. Version 6 (2002) introduced CWS zlib compression and AS2 components. Version 9 (2006) introduced ActionScript 3 (AVM2). Version 13 (2012) introduced ZWS LZMA compression. Re-saving never raises the version — that would require re-authoring in a Flash authoring tool — but it can re-pack within whatever the source version allowed.
Why is my "compressed" SWF larger than the original?
If the source was already ZWS-LZMA and you re-save as Very High quality with FWS uncompressed selected, the file will balloon by 2-4x. Make sure File Compression is set to a value lower than the source: Specific file size with a megabyte cap, or a lower Quality Preset. Also check that Resolution Percentage isn't accidentally set above 100%.
Can I batch-process a folder of SWF files?
Yes. Upload multiple .swf files in one session and the same settings apply to every file — useful for an e-learning library or a set of Flash videos. Each output downloads individually or in a zip.
Is my SWF file private?
Yes. Files are processed on our servers over HTTPS and auto-purged within hours — we never index them, never serve them publicly, and never train models on them. For especially sensitive archives, you can also compress SWF — files are uploaded over HTTPS, processed on our servers, and auto-deleted afterward.
Does this work for SWF files older than 2006?
Only if they contain video. SWFs from 1996-2005 are mostly vector animation with AVM1 (ActionScript 1 and 2), which has nothing to re-encode here — we tell you right after upload. Ruffle plays those almost completely, so keep the original file and open it in Ruffle.