This has been discussed A LOT on this forum. You provide no information on the type of COMAND, car, year, or anything else - since you are on the W220 forum and apparently can see TV when stationary (assumptions), I assume you have a US spec COMAND, DVD-based Nav system, and a DVD player capability. If that is true, you will not be able to set the COMAND to play while driving; some companies offer options to modify some COMANDS to add a TV tuner. You might search for that.
If you have a European spec COMAND, and a TV button, your COMAND can be set to display video while driving using the STAR diagnostics computer. Dealers and some specialty businesses have those.
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