Seamless-loop APNG: Netscape GIF loops and APNG `num_plays` plus last-frame dispose are not identical—migrations often lose a cycle or flash a seam
`loop-gif-apng` covers loaders, like pulses, and breathing highlights that must meet head-to-tail. GIF couples infinite-loop tags with disposal clears; APNG uses play counts and dispose/blend on an accumulating buffer—bad mapping leaves half-frame residue or a tempo jump. These clips loop forever, so low-power modes may freeze them. QA should count whole cycles with a stopwatch, not only confirm motion exists.
Loop variant: document finite vs infinite, align first/last dispose, then regress low-power and reduced-motion
- Record source loop count (0 = infinite in GIF) and the last frame’s disposal, then set the target APNG `num_plays`; if marketing needs “exactly three plays,” encode the integer explicitly—do not rely on encoder defaults.
- Step frame-by-frame across the boundary before frame 0; fix bright seams or alpha flashes by clearing the buffer or adjusting blend so the loop visually closes.
- Record 30s on devices with low battery mode and “Reduce Motion,” confirming the chosen degradation matches design instead of silently freezing on frame one.
Loop FAQ: play counts, seam flashes, power-saving behavior
Source GIF loops forever but APNG stops on the last frame—bad `num_plays=1` or a player bug?
Hex-inspect `acTL.num_plays` (0 often means infinite—confirm your encoder’s spec). If metadata is right yet playback stops, reproduce in stock Safari/Chrome to rule out custom decoders; attach frame index and dispose logs for the client team.
Every loop shows a white flash at the wrap—should frame 0 avoid blend or should the last frame clear to background?
Usually the buffer is not cleared at the boundary, so residue composites oddly. Try full dispose on the frame before the loop point or make frame 0 `blend_source` against a matching matte. Test on checkerboard and solid white—flashes often show on only one background.
We need three plays then hold the final frame for a confirm tap—can one APNG express that or do we need JS?
Set `num_plays` to three with correct terminal dispose when players honor it; many WebViews ignore counts, so add `animationend` listeners or fall back to video. Never assume universal `num_plays` support for transactional UI.
Motion feels faster in production than in design tools—lost delays or a global animation throttle?
Verify each `delay_num/delay_den` against GIF centiseconds; check accidental CSS `steps()` layering. If only some devices drift, log accessibility animation-scale settings.
Rich push needs a format APNG cannot satisfy—what parallel asset should we ship?
Many push surfaces want stills or short MP4/WebP; keep APNG for the web, generate square crops or six-second loops per channel spec. Maintain a channel matrix so one URL is not forced into every surface.