VBrick Systems VB6000, VB4000, VB5000 manual Stream Prioritization

Chapter 9

Stream Prioritization

Topics in this chapter

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Stream Prioritization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

How the WM Appliance Creates Priority Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

Configuring Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Overview

This section is written for network administrators who are configuring MBR (Multiple Bit Rate) streams on a VBrick encoder. It explains what streams and groups a WM player will play under certain predictable circumstances. It also provides details about how Groups should be configured. In particular, this document explains how to create a priority list in a Stream Prioritization Object. Depending on the streams being delivered, a Stream Prioritization Object may be created for a given server application whenever there are two or more streams present. The Windows Media server and VBrick appliances use priority lists in different ways to play streams:

•Windows Media server – the streams can be (1) pulled by the server from a VBrick, (2) pushed from the VBrick to the server, or (3) transferred in an archived file to a VOD publishing point on the server.

•VBrick Appliance – the streams are packaged in MBR Groups 1, 2, and 3.

Note The Stream Prioritization Object is defined in the Microsoft ASF specification. This discussion is based on VBrick's understanding of how the Stream Prioritization Object is designed to work.

Stream Prioritization

To select streams offered by a server, the WM Player (the "client") uses an item known as a Stream Prioritization Object. The Stream Prioritization Object is one of the many ASF protocol items sent from a server to its clients and this section describes VBrick's usage of the Stream Prioritization Object. The Stream Prioritization Object contains a list of offered streams, in which the order of the streams indicates priority: the first stream in the list has the highest priority and the last stream has the lowest priority. We will refer to the list of streams just mentioned as the "priority list," even though bitrate rather than priority is the vital consideration. To see how the priority list is utilized, we will consider a series of examples, starting with the situation in which no bitrate constraint is imposed by the WM Player.

Note The Stream Prioritization Object is automatically created by a VBrick appliance and sent to downstream WM players. It can also be created by a Windows Media Server.

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