Comparing AVIF to GIF.

Original HEVC/H.265 encoded video (1.1MB)

WebM (1.1MB)

WebP (1.0MB)

AVIF (400KB)

GIF (4.5MB)

Conversion commands:

AVIF (settings recommended by Gemini)

 ffmpeg -i banner_top.av1.mov \
      -c:v libaom-av1 \
      -crf 38 \
      -tile-columns 2 \
      -tiles 4x1 \
      -b:v 400k \
      -maxrate 800k \
      -cpu-used 4 \
      -enable-cdef 0 \
      -enable-global-motion 0 \
      -denoise-noise-level 0 \
      -pix_fmt yuv420p \
      test4.avif

I found on Webkit (iOS web rendering that powers both Safari and iOS Chrome), there were some playback issues (very slightly reduced framerate during portions of the 7 second clip). I found that reducing the number of encoded features (and using tiles) alleviated this issue.

GIF (settings recommended by Gemini)

 ffmpeg -i banner_top.av1.mov -filter_complex \
     "[0:v] split [a][b]; \
     [a] palettegen=stats_mode=full [p]; \
     [b][p] paletteuse=dither=sierra2_4a" \
     -loop 0 output.gif

WebP

ffmpeg -i banner_top.av1.mov \
    -c:v libwebp \
    -lossless 0 \
    -q:v 75 \
    -loop 0 \
    -vsync 0 \
    test.webp

WebM

ffmpeg -i banner_top.av1.mov \
    -c:v libvpx-vp9 \
    -pix_fmt yuva420p \
    -crf 20 -b:v 0 \
    -an \
    test.webm