, i.e. "I", "P," and "B" frames, one may conclude that there will be variations in sizes of frames of different types as well as of the same type due to different video content and different compression possibilities. So, all digital video content is compressed with source (statistical) coding techniques before transmission (or such video files are stored on video content servers), which results in highly varying bitrates for video. Because video traffic has high peak to mean ratio, in telecommunication networks it may be shaped (up to predefined maximum bitrates), which is typical in cases when video content over managed IP-based networks (not part of the public Internet) is pro- vided with QoS guarantees end-to-end (e.g. IPTV services provided by telecom opera- tors). Such video traffic shaping is shown in Figure 2.5. At the receiving side, the application (e.g. video player) buffers the video data with the aim of ensuring consistency in the reproduction of the video content. So, playback point is introduced with a certain delay in respect of the average delay of the packets to compensate for the delay variation of most of the packets. Figure 2.6 shows the typi- cal positioning of the playback point and typical probability distribution function of IP packet delays for video traffic. It is up to the video player to calculate the playback point to provide smooth watching of the content by the end-user (however, this is dependent upon the availability of consistent bitrate end-to-end from the video sender downstream to the video player of the end-user). 2 Internet QoS Key frames Peak bitrate (e.g. "I" frames in MPEG) Average Delta frames bitrate (e.g. "P" and "B" frames in MPEG) MPEG - Moving pictures experts group Figure 2.5 Video traffic shaping and effect of the packet delay. Average delay of Playback video packets point Video player application buffers packets to ensure consistent video delivery Video packets delay Figure 2.6 Video playback point. Most of the live video traffic is based on the RTP/UDP/IP proto