diff --git a/gst/compositor/compositor.c b/gst/compositor/compositor.c
index e2b212f821..f6a7f47654 100644
--- a/gst/compositor/compositor.c
+++ b/gst/compositor/compositor.c
@@ -265,6 +265,9 @@ _mixer_pad_get_output_size (GstCompositorPad * comp_pad, gint out_par_n,
       pad_height, dar_n, dar_d, GST_VIDEO_INFO_PAR_N (&vagg_pad->info),
       GST_VIDEO_INFO_PAR_D (&vagg_pad->info), out_par_n, out_par_d);
 
+  /* Pick either height or width, whichever is an integer multiple of the
+   * display aspect ratio. However, prefer preserving the height to account
+   * for interlaced video. */
   if (pad_height % dar_n == 0) {
     pad_width = gst_util_uint64_scale_int (pad_height, dar_n, dar_d);
   } else if (pad_width % dar_d == 0) {
@@ -368,8 +371,6 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
     /* We don't need to clamp the coords of the second rectangle */
     frame2_rect.x = cpad2->xpos;
     frame2_rect.y = cpad2->ypos;
-    /* This is effectively what set_info and the above conversion
-     * code do to calculate the desired width/height */
     frame2_rect.w = pad2_width;
     frame2_rect.h = pad2_height;
 
diff --git a/gst/compositor/compositor.h b/gst/compositor/compositor.h
index 5e8d90c82e..0c2c0a3ff1 100644
--- a/gst/compositor/compositor.h
+++ b/gst/compositor/compositor.h
@@ -104,6 +104,9 @@ struct _GstCompositor
   GstVideoAggregator videoaggregator;
   GstCompositorBackground background;
 
+  /* The 'blend' compositing function does not preserve the alpha value of the
+   * background, while 'overlay' does; i.e., COMPOSITOR_OPERATOR_ADD is the
+   * same as COMPOSITOR_OPERATOR_OVER when using the 'blend' BlendFunction. */
   BlendFunction blend, overlay;
   FillCheckerFunction fill_checker;
   FillColorFunction fill_color;