Do DVD players read from the outside in?

Question

I just bought a DVD and when I opened it, it was dislodged in the case. There is a scratch near the rim of the DVD. If I watch the beginning of the DVD and it doesn't skip will I know that it is okay? Meaning, does a DVD player read from the outside to the center?

Thanks!

Answer 1

DVD players do not always read DVD-Video discs in one direction...

There are four ECMA Standard 120mm DVD-ROM disk types:
    Type A* (aka DVD-5). Single Layer / Single-Sided
    Type B* (aka DVD-10). Single Layer / Double-Sided
    Type C (aka DVD-9). Double Layer / Single-Sided
    Type D (aka DVD-18). Double Layer / Double-Sided

*(Type A and B discs use PTP track mode only – see below.)

A DVD Read-Only disk contains a single physical "Volume Space" (and a single partition) per disk side. (The "Volume Space" is the usable area where digital data is stored.)

A Volume Space is comprised of one or two physical layers each containing a single, continuous spiral track structure. The track structure consists of contiguous, sequentially ordered (2048 byte) "logical sectors" and "physical sectors" where data is stored. Together the layer and track structure forms one of three types of physical volume space formats (or Track Modes) per side:

(a) Single-layer type -
Data is read from the inside of the disk (nearest the drive spindle) to the outside of the disk.

(b) Dual-layer type with parallel track path* (PTP) -
Data is read from the inside to the outside of the disk for each track on each layer (Layer 0 and Layer 1).

(c) Dual-Layer type with opposite track path (OTP) -
On the first layer (Layer 0) data is read from the spiral track beginning on the inside of the disk (nearest the drive spindle) and continuing toward the outside of the disk. On the second layer (Layer 1) data is read from the spiral track beginning near the outside of the disk and continuing toward the inside of the disk. (OTP is also commonly known as RSDL or reverse-spiral dual layer.)

The "Information Zone" (i.e., Lead-in Zone, Data Zone, and Lead-out Zone) spans a section of the disc between the diameters of 45mm (approx.) and 116mm; the length of the Data Zone can vary between 68mm and 116mm. It is also worth noting that "in practice, the lengths of the Data Zones of both layers are independent from each other."

Optical disc players use fairly robust error correction to counter various disc defects or damage that may occur such as scratches. The ability of the player's error correction to mask disc damage such as a scratch will, among other things, depend on the orientation and severity of the scratch; some disc players fair better than others.

If your disc is a dual-layer OTP disc (likely if it's a long-running large production movie, and/or has a menu option for anamorphic widescreen or letterbox versions, and/or contains two serial numbers on one side,) be sure and check the video playback near the point where Layer 0 changes to Layer 1. If needed you should be able to find the layer change time by searching the Internet using the title of your disc (in double quotes) along with the additional search term +“layer change”.

IMDb - DVDs by Disc Format
http://www.imdb.com/Sections/DVDs/DiscFormats/

DVD Review Layer Change List
http://www.dvdreview.com/movies/html/rsdl_list.html
http://www.dvdreview.com/movies/FilmVault.html
 

Answer 2

Hi. The laser inside the DVD player actually reads from the inside of the disk to the edge .When you load a DVD disk into your player the laser reads all the information such as no.of tracks, total time, sound format, etc. which is recorded near the center of the disc,If the scratch is perpendicular to the groove and it is not very deep the laser should not have any trouble it fills in the missing information. But if the scratch is across the surface in the direction of the grooves then you may experience a problem
There is a product you can buy that fills in the scratch,but i haven't used it myself.Hope this helps.