avfilter/vf_scale: fix interlaced chroma for other formats

This logic only covers the case of yuv420p. Extend this logic to cover
*all* vertically subsampled YUV formats, which require the same
interlaced scaling logic.

Fortunately, we can get away with re-using the same code for both JPEG
and MPEG range YUV, because the only difference here is the horizontal
alignment. (Which I omit touching for now, to avoid introducing possibly
unintended changes in default behavior)

libavfilter/vf_scale.c

@@ -518,6 +518,7 @@ static int config_props(AVFilterLink *outlink)
                             outlink->src->inputs[0];
     enum AVPixelFormat outfmt = outlink->format;
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
+    const AVPixFmtDescriptor *outdesc = av_pix_fmt_desc_get(outfmt);
     ScaleContext *scale = ctx->priv;
     uint8_t *flags_val = NULL;
     int ret;
@@ -588,14 +589,15 @@ static int config_props(AVFilterLink *outlink)
                 av_opt_set_int(s, "dst_range",
                                scale->out_range == AVCOL_RANGE_JPEG, 0);
 
-            /* Override YUV420P default settings to have the correct (MPEG-2) chroma positions
+            /* Override chroma location default settings to have the correct
-             * MPEG-2 chroma positions are used by convention
+             * chroma positions. MPEG chroma positions are used by convention.
-             * XXX: support other 4:2:0 pixel formats */
+             * Note that this works for both MPEG-1/JPEG and MPEG-2/4 chroma
-            if (inlink0->format == AV_PIX_FMT_YUV420P && scale->in_v_chr_pos == -513) {
+             * locations, since they share a vertical alignment */
+            if (desc->log2_chroma_h == 1 && scale->in_v_chr_pos == -513) {
                 in_v_chr_pos = (i == 0) ? 128 : (i == 1) ? 64 : 192;
             }
 
-            if (outlink->format == AV_PIX_FMT_YUV420P && scale->out_v_chr_pos == -513) {
+            if (outdesc->log2_chroma_h == 1 && scale->out_v_chr_pos == -513) {
                 out_v_chr_pos = (i == 0) ? 128 : (i == 1) ? 64 : 192;
             }