+ /*
+ * We use explicit/hierarchical signaling for LOAS.
+ * Other than that, we request implicit signaling to FDK library, then
+ * append explicit/backward-compatible signaling to ASC in case of MP4FF.
+ *
+ * Explicit/backward-compatible signaling of SBR is the most recommended
+ * way in MPEG4 part3 spec, and seems the only way supported by iTunes.
+ * Since FDK library does not support it, we have to do it on our side.
+ */
+ params.sbr_signaling = (params.transport_format == TT_MP4_LOAS) ? 2 : 0;
+