15. Discussion

Using a notebook to playback a video DVD has about the same kind of effect on battery lifetime as does audio CD playback. With our test system, we lost between 35 and 46%% of the battery lifetime for the idle mode test when playing back DVDs. Obviously, only a portion of the battery's energy went directly to the optical drive itself (about 4.5 watts). The rest, which varied from three to eight watts, depending on the player software we used, went to decoding activity in the CPU, chipset and RAM in the notebook.

Intervideo's WinDVD achieved the longest battery life in our testing. This player ran about 20 minutes longer than our other tests, such as Windows Media Player 10 for example.

Optimized for mobile PC use: Intervideo's WinDVD

It is clear that Intervideo expended the most brainpower toward making the best possible use of multimedia devices in a mobile PC, and also optimized its decoder code for use in notebooks. As a result, the CPU in a notebook works more efficiently, thus conserving more power than other DVD software.

There's no obvious explanation why playing back a video direct from the hard disk isn't more energy efficient than conventional playback from an optical drive. In fact, the hard disk consumes 1.5 watts during DVD playback (300 mA at 5 V), and the optical drive consumes 4.5 watts (910 mA at 5 V) doing the same thing.