This chapter focuses on the time system used by the decoder at the end user side to replicate the encoder’s clock system to accomplish a synchronized media play-out at end user side. The time system usually uses tools such as clock references and timestamps coded within the media stream. This chapter does not go into detail of the protocols used in IP networks to perform the media delivery, but it explains in detail the time-related fields coded within the media streams which are used at the user side decoder to provide a synchronized media play-out. The principal Moving Picture Experts Group (MPEG) media standards and their time system are described in this chapter. That includes MPEG-2 Transport Streams (MP2T), MPEG-4, MPEG Dynamic Adaptive Streaming over HTTP (MPEG-DASH), and MPEG Media Transport (MMT). This chapter also details the time information used by Digital Video Broadcasting (DVB) which is broadly used in multiple media delivery systems and used hand in hand with MPEG standards. First of all, this chapter describes the synchronization between video–audio media streams (lip sync) within a program in MP2T, and secondly, the synchronization between multiple programs, delivered within a multiplexed single MP2T stream. Secondly, this chapter describes timing issues in MPEG-4, which utilizes a different timeline system from MP2T to implement clock references and timestamps, as it is an object-oriented multimedia standard. Thirdly, this chapter describes timing issues in MPEG-DASH, which is an Adaptive Streaming over HTTP protocol widely used over the Internet. Additionally, this chapter also describes the time transmission in DVB systems, which use MP2T as a media container. The tools used are the DVB Service Information (DVB SI) and MPEG-2 Program-Specific Information (MPEG-2 PSI) tables. Finally, this chapter introduces the latest MPEG standard for media delivery, MMT, which aims to be a unique media delivery standard for heterogeneous networks, broadband technologies used in Internet TV and IPTV (Internet TV refers in this chapter to media delivery over a public non-managed IP network, such as Internet, and IPTV refers to media delivery over a private, managed IP network media delivery). It has also been proposed for broadcast (DVB) media delivery.
KeywordsMedia delivery systems Media delivery technologies Time system Media systems
Time information, clock references and timestamps, to reproduce, time-align encoder/source media clock to the decoder/receiver media clock.
A timestamp is used to agree on a specific moment in time, such as decoding, composing or playing time of an Access Unit (AU) or Media Access Unit (MDU).
They are the mechanism to recreate encoder’s clock frequency at the decoder to guarantee the correct media stream play-out, the means used by MPEG standards to reproduce encoder’s clock rate at the decoder.
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