For those of us who want more than what the Random/ Shuffle playback mode offers, the DVD specification has the virtual machine command "Rnd" which can generate a random number between 1 and a specified value. The maximum range is from 1 to 65535. The following example illustrates how to play these sixteen chapters randomly and not repeating the last three chapters already played in the random sequence. These are the additional steps we need to perform:

1. We add a cell command to each chapter. The cell command executes the postcommand section of the title PGC. The postcommand simply links to our random generator engine.

2. We need to create an additional PGC labeled "Random" whose precommand section contains the instructions to generate the random chapter (the chapter number is stored in GPRM0). The last three chapters played are stored in GPRM1, GPRM2, and GPRM3. When a new random value is generated, it is compared to one of these three values. If the chapter is already played back, the random generation process is repeated until a good value is produced. The contents of GPRM1, GPRM2, and GPRM3 are updated to reflect the most recent three chapters.

3. To separate the functions of random generation and the actual selection of the chapters to play back, we need to create another PGC labeled "RandomRouting" as following. The idea is that we can apply changes to our random generation algorithms within the precommand section of the PGC labeled "Random". The result value in GPRM0 is then passed to the PGC labeled "RandomRouting" to select the appropriate chapter to play back.

If everything is set up correctly, we should see the following link relationships as in the scenario below. To add or modify virtual commands, position the cursor at the appropriate Cell, Pre, or Post icons and double click to display the Simulation window. Otherwise, we can proceed to the Layout window to generate the VIDEO_TS folder.

The following display from the Simulation window allows the modification of virtual machine commands in the random generation engine (double click on the precommand section of the PGC label "Random").

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