VBrick Systems VB6000, VB4000, VB5000 manual Configuring Groups, Safe Group Configurations

2.Make a "V" list of streams, by following the same procedure used for making the A list, but with the terms "audio" and "video" swapped.

3.Make the priority list be the A list, if the lowest-bitrate audio stream included in the multiplexing application has bitrate less than the lowest-bitrate video stream included in the multiplexing application; otherwise, make the priority list be the V list.

4.If the script stream is included in the multiplexing application, then insert the script stream as the second-highest priority stream in the priority list.

Configuring Groups

In the case when all enabled MBR Groups contain both audio and video streams, it is highly preferable for the MBR Groups to be configured so that the Groups’ audio bitrate and video bitrate are in the same order. For instance, if Group 2 has the highest video bitrate, Group1 has the next highest video bitrate, and Group3 has the lowest video bitrate, then Group 2 should have the highest audio bitrate, Group 1 should have the next highest audio bitrate, and Group 3 should have the lowest audio bitrate. (Ties are allowed.) Given the "greedy" nature of the Player's stream selection algorithm, results become unpredictable otherwise. As an example, suppose that MBR Group1 and Group2 are enabled, with rates—in Kbps— selected this way.

Group1: audio rate is 192, video rate is 200.

Group2: audio rate is 128, video rate is 300.

The priority list is 200, 192, 300, 128. The Player asks for the 192Kbps audio stream and the 300Kbps video stream; i.e., Group1's audio stream together with Group2's video stream. As a result, the VBrick Server transmits nothing to the Player. On the other hand, suppose that the Groups are

Group1: audio rate is 192, video rate is 260.

Group2: audio rate is 128, video rate is 300.

The priority list is 300, 128, 260, 192. In this case, the Player asks for (and receives) Group1 from the VBrick Server—even though Group2's video rate is larger than Group1's video rate. Next, consider a case in which audio bitrates and video bitrates are in the same order.

Group1: audio rate is 128, video rate is 400.

Group2: audio rate is 192, video rate is 600.

The priority list is 400, 128, 600, 192. If the Player imposes a bandwidth restriction which is (roughly speaking) inside the range between 728 Kbps and 792 Kbps, then it will ask for Group1's audio stream and Group2's video stream. In this case, the Player will receive nothing from the VBrick Server.

Safe Group Configurations

The ambiguity problems described above do not exist when the MBR Groups are collectively video-only, or when they're collectively audio-only. They also do not exist when all MBR Groups share either one common audio stream, or one common video stream. There is also this configuration, based on using a low-rate audio encoder and a high-rate audio encoder, a low-rate video encoder and a high-rate video encoder.

Group1: low-rate audio, low-rate video.

Group2: low-rate audio, high-rate video.

Group3: high rate audio, high-rate video.

140 © 2008 VBrick Systems, Inc.