DVD and Blu-ray Discs Specifications.

[Smokey]

This is an edited version of article from Crutchfield (link below).

If you place a DVD, and a Blu-ray Disc™ next to each other, they look nearly identical. But each formats has a different physical structure, data format, and error correction system. Below we'll discuss what makes a DVD different from a Bu-ray.

DVD:

All DVDs use a "sandwich" design — two 0.6-millimeter discs bonded together. This sandwich construction allows DVD discs to have information on both sides and on one or two layers per side. This design is also more structurally stable and resistant to disc warping.

Single-sided, single-layer: Even DVD discs with a single information layer can hold the complete audio and video for a full-length movie, including Dolby® Digital 5.1 soundtracks in three different languages. Total capacity: 4.4 gigabytes (over 2 hours of video).

Single-sided, dual-layer: This disc type has two information layers, providing nearly twice the data capacity of a single-layer DVD. The layer closer to the player's laser pickup has a semi-transparent coating. The laser is able to shine through this layer to read the deeper layer beneath it, then re-focus to read the semi-transparent layer. Total capacity: 8 gigabytes (about 4 hours of video).

Double-sided, dual-layer: This disc type provides the maximum data capacity. It's basically two single-sided, dual-layer discs bonded together. As with all double-sided DVDs, you'll have to flip the DVD over yourself. Total capacity: 15.9 gigabytes (over 8 hours of video).

Blu-ray Discs:

Blu-ray discs have capacity of 25GB (dual-layer 50GB) with maximum data transfer rate of 54 Mbps (DVD have rate of 11 Mega-byte-per-second). The developers of Blu-ray couldn't make the disc physically larger, so the information pits got smaller, and the spacing of the pit rows got tighter.

In order to read these much smaller data pits, Blu-ray players use a blue-violet laser, which has a shorter wavelength and a smaller "beam spot" than the red laser used in DVD players. The players also spin the discs at higher speeds for even faster data transfer.

The discs also have a super-thin transparent protective coating, which places the data layer closer to the disc's surface and thus closer to the laser.

Codecs:

Compression is what made video formats like DVD and HDTV possible/ The digital data is compressed for encoding on a disc, and then decompressed by your player. These compression/decompression technologies are often referred to as "codecs" for short.

MPEG-2 is the video codec used for DVDs and current HDTV content, including broadcast, cable and most satellite TV. Blu-ray also uses MPEG-2, as well as two newer, higher-efficiency codecs: AVC MPEG-4 and VC-1 (based on Windows Media Video 9).

As for audio, Dolby Digital Plus, offers up to 7.1-channel surround sound for even more enveloping audio than standard 5.1-channel Dolby Digital. There are even "lossless" options, Dolby TrueHD and DTS-HD Master Audio, which deliver the closest possible reproduction of the movie studio's original master.

Many Blu-ray titles feature multichannel LPCM soundtracks — uncompressed audio that should also match the quality of the studio master.

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