Set CD Graphics palette opaque.

libavcodec/cdgraphics.c

@@ -126,7 +126,7 @@ static void cdg_load_palette(CDGraphicsContext *cc, uint8_t *data, int low)
         r = ((color >> 8) & 0x000F) * 17;
         g = ((color >> 4) & 0x000F) * 17;
         b = ((color     ) & 0x000F) * 17;
-        palette[i + array_offset] = r << 16 | g << 8 | b;
+        palette[i + array_offset] = 0xFF << 24 | r << 16 | g << 8 | b;
     }
     cc->frame.palette_has_changed = 1;
 }