libx264: Allow Stereo3D monoscopic value

libavcodec/libx264.c

@@ -209,6 +209,11 @@ static void reconfig_encoder(AVCodecContext *ctx, const AVFrame *frame)
         case AV_STEREO3D_FRAMESEQUENCE:
             fpa_type = 5;
             break;
+#if X264_BUILD >= 145
+        case AV_STEREO3D_2D:
+            fpa_type = 6;
+            break;
+#endif
         default:
             fpa_type = -1;
             break;