AVIF_CHROMA_UPSAMPLING_AUTOMATIC doesn't use kFilterBilinear with libyuv functions after commit 95d96ea6c8428e6c796b94f880b6e7a5979cb3a3

[wantehchang]

A bug was introduced in commit 95d96ea (#1264). Here is the relevant code before and after the commit.

Before:

            const enum FilterMode filter = ((rgb->chromaUpsampling == AVIF_CHROMA_UPSAMPLING_FASTEST) ||
                                            (rgb->chromaUpsampling == AVIF_CHROMA_UPSAMPLING_NEAREST))
                                               ? kFilterNone
                                               : kFilterBilinear;

After:

// Only allow nearest-neighbor filter if explicitly specified or left as default.
static avifBool nearestNeighborFilterAllowed(int chromaUpsampling)
{
    return chromaUpsampling != AVIF_CHROMA_UPSAMPLING_BILINEAR && chromaUpsampling != AVIF_CHROMA_UPSAMPLING_BEST_QUALITY;
}

...

const enum FilterMode filter = nearestNeighborFilterAllowed(rgb->chromaUpsampling) ? kFilterNone : kFilterBilinear;

Suppose rgb->chromaUpsampling is AVIF_CHROMA_UPSAMPLING_AUTOMATIC. Before the commit, filter is set equal to kFilterBilinear. After the commit, filter is set equal to kFilterNone.

The effect of the bug is that AVIF_CHROMA_UPSAMPLING_AUTOMATIC doesn't use kFilterBilinear with libyuv functions.

I will write a fix.