--- a/dom/media/platforms/agnostic/AOMDecoder.cpp
+++ b/dom/media/platforms/agnostic/AOMDecoder.cpp
@@ -133,16 +133,17 @@ highbd_img_downshift(aom_image_t *dst, a
   }
   switch (src->fmt) {
     case AOM_IMG_FMT_I42016:
     case AOM_IMG_FMT_I42216:
     case AOM_IMG_FMT_I44416:
     case AOM_IMG_FMT_I44016:
       break;
     default:
+      // We don't support anything that's not 16 bit
       return AOM_CODEC_UNSUP_BITSTREAM;
   }
   for (plane = 0; plane < 3; plane++) {
     int w = src->d_w;
     int h = src->d_h;
     int x, y;
     if (plane) {
       w = (w + src->x_chroma_shift) >> src->x_chroma_shift;