Animation is not compressed losslessly with YCgCo-Re

[y-guyon]

Reproduction instructions (0.png 1.png 2.png 3.png 4.png are in five_frames_of_okfestival2014_ascent_of_mrs_graham.zip and were taken from okfestival2014_ascent_of_mrs_graham.gif):

git clone https://github.com/AOMediaCodec/libavif.git
cd libavif
git checkout 5eaa316da9b101d5fdfe6939738670ef5610e9d5
cmake -S . -B build -DAVIF_BUILD_APPS=ON -DAVIF_CODEC_AOM=LOCAL -DAVIF_ENABLE_EXPERIMENTAL_YCGCO_R=ON -DAVIF_LIBYUV=LOCAL
cmake --build build --parallel
build/avifenc --speed 6 --lossless --cicp 2/2/16 0.png 1.png 2.png 3.png 4.png anim.avif
build/avifdec anim.avif --index 2 2.dec.png

2.dec.png differs from 2.png (I used ImageMagick):

compare 2.png 2.dec.png 2.diff.png  # Shows two red dots near the hot-air balloon.

For example, the pixel located at 24,312 goes from RGB #efd3cb to #eed1c9.

Notes

• The issue appeared with other images.
• The issue disappeared when encoding only 0.png 1.png 2.png 3.png.
• The issue appeared at speeds 0,1,2,3,4,5,6.
• The issue did not appear at speeds 7,8,9. This makes me think of an issue in aom.
• Changing the codec at encoding was not possible because only aom supports encoding 4:4:4 lossless samples.
• Changing the codec at decoding did not fix the issue.

[y-guyon]

Compiler is GNU 14.2.0.

[y-guyon]

avifenc --help shows

Version: 1.1.1 (aom [enc/dec]:v3.11.0)
libyuv : available (1887)

[y-guyon]

Filed an issue at https://aomedia.issues.chromium.org/387472912

[y-guyon]

Same issue with aom 3.10.0, 3.9.1 and 3.8.3.