The accurate packet loss measurement of application traffic has been challenging, since the frequently-used active monitoring approaches that use probe packets cannot capture the packet loss experienced by the traffic of individual user applications. Moreover, measurement and estimation of packet loss characteristics are challenging due to the relatively rare occurrence and typically short duration of packet loss episodes. Because it is often impossible to measure the entire data passing across a network, the most widely used method of measurement works by injecting probe packets. In order to overcome these shortcomings, this paper based on the analysis of MPEG4 video structural features and RTP encapsulation strategy, a novel packet loss probing technique, packet loss measurement based on User_Data (PLBU), is proposed. The PLBU complete packets loss measurement by using User_Data field of MPEG-4 video. This does not affect the normal video playback and dose not need to inject new probing stream, which makes it, less intrusive. NIST Net and Planetlab experiments verify the effectiveness of this method, and show that PLBU estimates packet loss more accurately, and with less measurement overhead than other existing technique such as BADABING.