V210 issue fix + correct packing

internal/generator/text_test.go

@@ -163,7 +163,7 @@ func TestTextOverlayApplyV210(t *testing.T) {
 		t.Fatalf("NewTextOverlay: %v", err)
 	}
 
-	frame := make([]byte, frameW*frameH*8/3)
+	frame := make([]byte, V210FrameSize(frameW, frameH))
 	for i := range frame {
 		frame[i] = 0x5A // marker: untouched regions must survive
 	}
@@ -192,7 +192,7 @@ func TestTextOverlayApplyV210(t *testing.T) {
 		{o.x + o.w, o.y + o.h}, // corner
 		{100, 1000},            // far away
 	} {
-		off := ((p[1]*frameW + p[0]) / 6) * 16
+		off := p[1]*V210LineSize(frameW) + p[0]/6*16
 		for i := 0; i < 16; i++ {
 			if frame[off+i] != 0x5A {
 				t.Fatalf("block at (%d,%d) modified outside the box", p[0], p[1])