Listening to videos and battery life

Q: I like to play video concerts on my iPod just for the music, but the video drains the battery too fast. If I set the the iPod to TV out so that the video doesn’t show up on the screen, will this extend the battery life?

– Dave

A: This will extend the battery life, although on a hard-drive based iPod it will not be as much of an increase as you might expect.

The two major sources of battery drain on the iPod classic and prior models of hard-drive based iPod are the LCD backlight and the hard drive. Setting your videos to play audio only via the “TV Output” option will increase battery life by preventing the backlight from turning on, but will still have an impact on the hard drive.

The problem is that the hard-drive based iPod models conserve battery power through the use of a memory buffer—when listening to a playlist, the hard drive spins up, loads a certain amount of data into the buffer, and then spins down and goes to sleep. This means that most of the time the iPod is playing music from the memory buffer rather than accessing the hard drive.

Since the buffer is a finite size, however, the larger the original source track, the less information the buffer can contain—therefore the hard drive has to be read more often to refill the buffer.

For normal 128kbps music tracks, the buffer can hold approximately 30-60 minutes of music on a fifth-generation iPod or iPod classic. However, a video file is significantly larger, and even if you are not playing the video portion of the file, it still needs to be read into the iPod’s buffer. The result is that the hard drive needs to spin up considerably more often—generally every 5-10 minutes depending upon the bit-rate of the source video itself.

This same scenario applies to higher bit-rate audio tracks. For example, Apple Lossless and AIFF tracks have a dramatic effect on battery life as compared to 128kbps MP3/AAC tracks.

So while you will see some battery savings from not having the backlight on, the increased hard drive access is still going to drain your battery at a much faster rate than if you were listening to audio tracks.

If battery life is a primary concern, you may want to consider extracting the audio portion of these video tracks and transferring it to your iPod as a separate audio-only track. There are a number of video/audio editing tools out there that can be used to accomplish this for non-DRM-protected videos.

Note that this will not be a factor on flash-based iPod models such as the 2007 iPod nano (with video), or the iPod touch or iPhone. These models have no hard drive and are therefore more power-efficient in this regard. Unfortunately, these models also do not offer the ability to enable the TV Output feature without connecting a compatible accessory.