GIFs went through the still-image path, so an animated GIF came in as a
single frame with zero duration. A GIF with two or more frames is now
probed as a movie: its frame rate is chosen so every per-frame delay is
a whole number of frames (uneven timing is kept exactly), delays of 0
or 1 hundredths count as 10 like in browsers, and the pool decodes the
frame shown at the requested time. A single-frame GIF stays a still.
Co-Authored-By: Claude Sonnet 5.5 <[email protected]>