With the recent purchase of the eeePC, I have been thinking about the impact of video quality vs battery-life. The information below is theory, and has not been tested at this time.

My eeePC 900HD came equipped with a basic 3-cell battery, which, when I put it through it’s first movie, is not capable to play a 2 1/2 hour movie on a single charge. Because of this, I’ve been putting some thought on what affects batterylife during playback, and how the viewing experience can be enhanced.

*Brightness: One of the first, most logical things to keep in mind is the screen brightness. The brighter the screen is set, the more power it drains, and as a result, the battery drain is quite significant. Reducing the brightness will increase battery life significantly.

*Networking: a wireless networking connection takes power to establish and maintain a connection, and continiously puts strain on the battery as well. Turning it off while watching a movie will save battery life tremendously.

*Drive activity: the location of where you have the movie, or if there are programs running in the background. A harddrive or a cd/dvd drive all have moving parts, and when used for video playback they will be continuously be running to be able to run the movie. A Solid State disk, or even a flash card will reduce power useage due to the lack of moving parts.

The above is quite obvious, however, what many people do not realize is that the format of the video makes a huge impact as well.

H264/AVC Video is very processor-demanding. Some of the lower-end systems might even have issues playing video files in this format properly, and on all portable systems available at this time, the processor will need to run at full-speed to be able to keep a fluent playback. On portable devices, such as Apple’s iPod and iPhone devices, some newer Windows Mobile devices, and the upcoming Netbooks with Nvidia chips in them feature hardware acceleration for this video format, which reduces the strain on the processor enough to eliminate the need to run at full speed.

DIVX AVI is less processor demanding, but depending on the version used (DIVX5/DIVX6/DIVX7), there is a difference. DIVX6 and 7 include additional features to improve quality, which also increases processor demand. The DIVX codec options also include quality enhancement filters, such as “deblocking” and “deinterlace” which also put additional strain on the processor, keeping it running at full speed.

XVID AVI is a bit less straining on the processor than DIVX, but the Windows installer (Koepie’s version) does include various options for quality enhancement that are enabled by default.

MPEG1 MPEG2 is considerably less processor demanding than any of the other formats. Even very old computers (Pentium 1, 166Mhz) are capable  of playback of these files, but due to the bigger file size of these files, the hard drive speed comes in to play.

Windows Media WMV Depending on the format itself (VC1, WMV9, WMV8, WMV7) the processor requirements differ greatly. VC1 is used for HD video content, and while it offers great quality, the processor useage is quite high as well. WMV9, the non-HD variant of VC1 is less demanding on the processor, while maintaining a good quality. WMV8 uses less than WMV9, and WMV7 uses less than WMV8.

H263 3GP This format is specifically designed for Cellphones, and requires very little processor power, but results in terible quality on bigger screens.

The way the files are created plays a big difference in performance requirements. Due to its initial design for “portable” devices, DVD Catalyst does not use any real “advanced” options (cabac,quantisizers, degaus etc) for it’s normal conversions. While the “HQ” profiles do use some of them, the default profiles are optimized for sped and compatibility, resulting in faster conversions at good quality. For playback this also assists in battery-life. A basic rule that can be used is that the faster the conversion completes, the less battery-power it will use. This rule does not really apply to people who use the latest systems with the CoreI8 50Ghz 32-core processors, but for the average computer user it is a fairly safe indication.

Besides the compression format itself, the other difference between these is that to maintain the same quality the file-size is directly affected. The higher the processor requirement, the smaller the resulting file can be while maintaining the same visual quality. With the same screen size resolution settings, a H264/AVC video file can be about half the size of an XVID file of the same quality, and an MPEG2 file will be about 4x as big as an XVID file on the same visual quality.

While the file-size would theoretically be an additional battery drain, most video player applications actually “stream” the file from the harddrive. They continuously read from the file to direct it to the screen. So in most cases, it does not matter if the file is big or small, because the drive that actually contains the video file is still used during the whole time you are watching the movie. To eliminate this, a video player application would need to have a memorybuffer that would load a portion of the movie, and then stop accessing the drive until it hits a certain percentage in the buffer so it can load the new data again. In this case, the file size does make a difference, because the bigger the file, the more times the buffer needs to be filled. at a buffer of 64MB, if we have an MPEG2 movie of 4GB in size, or a 3GP movie of 120MB in size, the difference is considerably. The 3GP movie will only need to fill the buffer twice, once every hour if we are talking about a 2 hour movie, while the MPEG2 movie will have to fill the buffer 64 times, or about once every 2 minutes.