QUOTE (Arrattkak @ Mar 21 2010, 12:01 AM) Whenever i see a commercial for a movie coming out on dvd its like "out on dvd and blu ray" and i never new what blu ray was exactly, is it a kind of HD thing?
Think of it like dvd but higher quality much like HDTV is higher visual quality than what is now referred to as SDTV which is the normal resolution of older televisions. DVDs contain video that is about 720x480 pixels. Blu-rays contain either 720p or 1080p video which are 1280x720 or 1920x1080. This isn't quite true though as most new dvds and likely blu-rays as well actually come with video that is the same width but not as tall that imitates a theatre's screen so you will get things like 1280x540 or similar sizes.
The main difference between blu-ray and DVDs are it's size. The DVDs hold usually around 4.7 GB or 8.5 GB. A blu-ray disc holds 25 GB, 50 GB, or even 100 GB in data. This difference in data is what makes Final Fantasy XIII suck in the 360 and awesome in the PS3 (youtube comparison [see in 720 for better comparison]). The PS3 version goes full HD while the 360 version only upscales to 720 from 576. Not to mention the 360 doesn't have all the features of the PS3 game and the texture maps aren't as good, especially when you zoom in on an object up close. It can hold a lot more, which is important when it comes to video.
Most people are used to 120 MB-ish videos for 480p, 200 MB-ish videos for 720p, and upper 300MB-ish videos for 1080p here on FTV. These videos are actually compressed to reach this size. The actual size of the video inside DVDs or Blu-rays take up the whole size of the disc because they have a large bitrate and worse compression method. In other words, the DVDs and Blu-rays have videos that are larger in file size than necessary to hold in quality that isn't necessarily noticeable.
For instance, the DVD uses MPEG-2. One can have the same quality as a .h264 (which is what the majority of all the videos in FTV are encoded in) at double the size. Blu-ray on the other hand, uses .h264 but doesn't use all the options and has a higher bitrate for the videos than the ones used here on FTV.
Thus the size of a single DVD ripped can be 4 GB large and only 1 GB when compressed to how most here are used to watching on FTV. I think I'm straying off topic. Anyways, as Langes01x has said, DVDs are normally 480p and Blu-rays are 720p or 1080p because of this size difference.