Q. When it comes to streaming and downloading movies, do you really notice that much of a difference between standard definition and the high-definition version?
A. High-definition (HD) files pack considerably more pixels into the video than those classified as standard definition (SD), and in side-by-side comparisons, the sharpness of the picture and depth of the colors in an HD video can stand out. You may want to sample both formats on a similar type of movie and see which version you prefer.
Online video services typically label movies by the number of pixels in their vertical dimension; more pixels generally mean a sharper picture. HD movies are usually classified as 1,080p or 720p (referring to the resolutions of 1,280 by 720 pixels or 1,920 by 1,080 pixels). Movies in standard definition have lower resolutions and can vary based on the provider, but a sample SD movie downloaded from iTunes has a resolution of 853 by 352 pixels.
If you are watching the movie on a small tablet, phone or other screen, SD video quality is usually just fine. Standard-definition videos are less expensive to buy, often by about $5, and $1 or $2 less to rent in some online stores. Certain devices cannot fully display HD video anyway because the screens lack the needed resolution or the hardware is not compatible. (Some files may automatically download in standard definition anyway depending on the device you are using.)
Because they contain more data, downloaded HD videos need more bandwidth to stream and, when downloaded, take up more space on your device. For example, the 720p HD version of “The Martian” in Apple’s iTunes Store is a 5.36-gigabyte file, while the SD edition weighs in at 2.54 gigabytes. If you are downloading a movie to a mobile device to watch offline, the SD edition is a space saver. If you plan to watch the movie on a high-definition television or high-resolution computer monitor, though, SD video can look flatter and less vibrant than the HD version.
Many video services are now offering movies and television shows in yet another format: ultra high-definition, also known as “4K” for its 3,840 by 2,160 pixels of resolution. Amazon, Apple, Google, Microsoft, Netflix, Roku, Vudu and YouTube are among the services with 4K content or devices; video in the 4K H.D.R. (high dynamic range) format is also available from some services. To properly appreciate the clarity and color depth of the newer formats, you need a TV or monitor that can actually display 4K or 4K H.D.R. video — and a lot more bandwidth to stream or store the file.
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