VBrick Systems VB4000, VB6000, VB5000 manual Non Bitrate Constrained, Example 1 - Priority List

Non Bitrate Constrained

Example 1 – Priority List

Suppose that the priority list is video1, audio1, video2, audio2, video3, audio3 (do not confuse the subscripts used here with Encoder MBR Selections). The WM Player identifies these five pairs: video1, audio1; audio1, video2; video2, audio2; audio2, video3; video3, audio3. This

approach to parsing a list is an example of what is sometimes called a sliding window. The WM Player selects the pair with the highest total bitrate. If the priority list is audio1, video1,

audio2, video2, audio3, video3, then the WM Player identifies the five pairs audio1, video1; video1, audio2; audio2, video2; video2, audio3; audio3, video3, and selects the pair with the highest total bitrate.

In these examples, the priority list contains an equal number of audio and video streams. This is not always the case, however. There can be fewer or more audio streams than video streams, and without further explanation, the term "sliding window" stops being appropriate.

Example 2 – Redundant List

Suppose that the priority list is video1, audio1, video2, audio2, audio3. How the WM Player parses this list can be illustrated by replacing the priority list with this redundant list: video1, audio1, video2, audio2, video2, audio3. The sliding window mechanism, applied to the redundant list, defines which pairs the WM Player identifies: video1, audio1; audio1, video2; video2, audio2; video2, audio3 (the pair audio2, video2 has been omitted, since it is the same as video2, audio2). Among the four pairs just mentioned, the WM Player selects the one with the highest total bitrate.

As another example, the redundant list corresponding to the priority list audio1, video1, video2, video3, is audio1, video1, audio1, video2, audio1, video3. The WM Player identifies the three pairs audio1, video1; audio1, video2; audio1, video3, and it selects the pair with the highest total bitrate. In the case of a video-only or audio-only priority list, the highest-bitrate stream is selected.

Example 3 – Script Stream

There is one more stream to be considered: the script stream. The script stream includes metadata and closed captioning if they are enabled on the Video page, and if Closed Caption and Metadata is checked on the Server page. If the server offers the script stream, then the WM Player will consider it.

Bitrate Constrained

So far, we have described the situation in which no bitrate constraint is imposed by the WM Player. Now we turn our attention to what happens when the WM Player imposes a bitrate constraint. The discussion will assume that the WM Player considers the script stream, when it is offered. The broad statement to be made is that the WM Player traverses the priority list, starting at the highest-priority stream, and stops immediately before the bitrate constraint is exceeded. (Note: the bitrate constraint imposed by the WM Player is, in general, slightly smaller than the value appearing in the URL modifier.) One particular consequence is that the WM Player might not select one stream of each type offered, where "type" means audio, video, or script.

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