This is the only tool here that has to preserve motion, which makes it the most involved. Every other converter decodes one picture and re-encodes it. This one pulls apart an animation frame by frame, rebuilds each frame’s colours from scratch, and reassembles the whole thing with its timing intact.
You are trading colour for compatibility
APNG is technically the better format. It stores full 24-bit colour with smooth 8-bit transparency, exactly like a still PNG. GIF allows 256 colours per frame and transparency that is strictly on or off. Converting therefore means quantising every frame down to a 256-colour palette, and on gradients or photographic content you will see the difference as banding or a fine speckled dither.
The reason to do it anyway is that GIF goes places APNG does not. Plenty of chat apps, forums, older email clients, presentation software and upload forms accept GIF and either reject an APNG or, worse, display only its first frame as a still image.
What is preserved and what changes
- Frame timing is carried across. APNG stores delays in milliseconds and GIF in hundredths of a second, so timings are rounded to the nearest centisecond.
- Very short delays are raised to a floor of about 20 milliseconds, because GIF cannot express faster and browsers clamp them anyway.
- Soft transparency becomes hard transparency. Semi-transparent pixels are forced fully visible or fully invisible, so feathered edges and drop shadows gain a jagged outline.
- Each frame gets its own palette, which costs a little file size but stops a colour-shifting animation from banding badly on later frames.
Expect the GIF to be larger
People are often surprised by this, since GIF has fewer colours. But APNG inherits PNG’s compression, which is considerably better than the LZW scheme GIF has used since 1987, and it can store only the changed region of each frame. A GIF of the same animation is commonly two to four times bigger. If size is what you care about and the destination supports it, a short video or WebP animation beats both.
If your file is not animated
An APNG is a normal PNG with extra animation chunks, so a still PNG is a perfectly valid input that would produce a one-frame GIF. That is almost never what anyone wants, so the tool detects it and says so rather than handing you a static file. Conversion runs in a background thread on your own device, and nothing is uploaded.