Why define SrsRtspPacketPayloadType instead of SrsRtpPacketPayloadType?

[suzp1984]

srs/trunk/src/kernel/srs_kernel_rtc_rtp.hpp

Lines 251 to 270 in ce2ce15

	// The payload type, for performance to avoid dynamic cast.
	enum SrsRtspPacketPayloadType
	{
	SrsRtspPacketPayloadTypeRaw,
	SrsRtspPacketPayloadTypeFUA2,
	SrsRtspPacketPayloadTypeFUA,
	SrsRtspPacketPayloadTypeNALU,
	SrsRtspPacketPayloadTypeSTAP,
	SrsRtspPacketPayloadTypeUnknown,
	};
	class ISrsRtspPacketDecodeHandler
	{
	public:
	ISrsRtspPacketDecodeHandler();
	virtual ~ISrsRtspPacketDecodeHandler();
	public:
	// We don't know the actual payload, so we depends on external handler.
	virtual void on_before_decode_payload(SrsRtpPacket* pkt, SrsBuffer* buf, ISrsRtpPayloader** ppayload, SrsRtspPacketPayloadType* ppt) = 0;
	};

I was confused when read above code, I don't understand why define SrsRtspPacketPayloadType instead of SrsRtpPacketPayloadType. I checked the commit git show a1d7fe46c1 and #2304 , maybe this is a mistake.