Editing Optical disc (section)

==Surface error scanning==
[[File:QPxTool DVD error rate graph.png|thumb|Error rate measurement on a DVD+R. The error rate is still within a healthy range.]]
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Optical media can [[Predictive failure analysis|predictively]] be scanned for errors and [[disc rot|media deterioration]] well before any data becomes unreadable.<ref name=qpx>{{Cite web|url=https://qpxtool.sourceforge.io/faq.html|title=QPxTool - check the quality|website=qpxtool.sourceforge.io|access-date=2020-07-06|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806024813/https://qpxtool.sourceforge.io/faq.html|url-status=live}}</ref> Optical formats include some redundancy for [[error correction]], which works until the amount of error exceeds a threshold. A higher rate of errors may indicate deteriorating and/or low quality media, physical damage, an unclean surface and/or media written using a defective optical drive.

Precise error scanning requires access to the raw, uncorrected readout of a disc, which is not always provided by a drive. As a result, support of this functionality varies per optical drive manufacturer and model. On ordinary drives without this functionality, it is possible to still look for unexpected reduction in read speed as an indirect, much less reliable measure.<ref name=QPx-Supported>{{cite web| url = https://qpxtool.sourceforge.io/supported.html| title = List of supported devices by disc quality scanning software QPxTool| access-date = 2020-07-06| archive-date = 2020-07-06| archive-url = https://web.archive.org/web/20200706162837/https://qpxtool.sourceforge.io/supported.html| url-status = live}}</ref>

Optical media, such as [[Compact disc|CDs]] and [[DVD|DVDs]], can be scanned to detect errors and signs of deterioration well before data becomes unreadable. These formats include built-in [[Error detection and correction|error correction]] mechanisms, which function by adding redundant data. However, once the rate of errors surpasses the correction threshold, the media becomes vulnerable to failure. A high error rate can signal physical deterioration, low-quality manufacturing, surface contamination, or data recorded by a faulty optical drive.

Accurate error scanning requires access to a disc's raw, uncorrected readout. However, not all optical drives provide this capability, and support for this feature can vary significantly between manufacturers and drive models. On drives lacking raw data access, users may rely on a less precise method: monitoring unexpected reductions in read speed, though this is a far less reliable indicator of disc health.

Several specialized tools are available for performing error scans on optical media. Popular programs include [[Nero DiscSpeed]], [[KProbe|K-Probe]], Opti Drive Control (previously known as "CD Speed 2000"), and DVD Info Pro for [[Windows]]. For cross-platform users, QPxTool is available to help monitor and maintain optical media integrity. Each of these tools allows for detailed analysis of the error rates and conditions affecting optical discs.

=== Error types ===
There are different types of error measurements, including so-called ''"C1"'', ''"[[C2 error|C2]]"'' and ''"CU"'' errors [[Compact disc#Measurement|on CDs]], and ''"PI/PO (parity inner/outer) errors"'' and the more critical [[DVD#Disc quality measurements|''"PI/PO failures"'' on DVDs]]. Finer-grain error measurements on CDs supported by very few optical drives are called ''E11'', ''E21'', ''E31'', ''E21'', ''E22'', ''E32''.

''"CU"'' and ''"POF"'' represent uncorrectable errors on data CDs and DVDs respectively, thus [[data loss]], and can be a result of too many consecutive smaller errors.<ref>{{cite web |title=QPxTool glossary |url=https://qpxtool.sourceforge.io/glossar.html |website=qpxtool.sourceforge.io |publisher=QPxTool |access-date=22 July 2020 |ref=QPx-Glossary |archive-date=1 August 2021 |archive-url=https://web.archive.org/web/20210801053045/https://qpxtool.sourceforge.io/glossar.html |url-status=live }}</ref>

Due to the weaker error correction used on [[Audio CD]]s ([[Compact Disc Digital Audio|Red Book]] standard) and [[Video CD]]s ([[White Book (CD standard)|White Book]] standard), [[C2 error]]s already lead to data loss. However, even with C2 errors, the damage is inaudible to some extent.

[[Blu-ray]] discs use so-called ''LDC'' (''Long Distance Code''s) and ''BIS'' (''Burst Indication Subcode''s) error parameters. According to the developer of the ''Opti Drive Control'' software, a disc can be considered healthy at an ''LDC'' error rate below 13 and ''BIS'' error rate below 15.<ref name="cdrinfo-BD">{{cite web |title=Blu-Ray Writing Quality Tests Vol 2 |url=https://www.cdrinfo.com/Sections/Reviews/Print.aspx?ArticleId=25532 |website=www.cdrinfo.com |publisher=CDR info |access-date=1 August 2020 |date=2009-06-19 |archive-date=2010-01-07 |archive-url=https://web.archive.org/web/20100107203123/https://www.cdrinfo.com/Sections/Reviews/Print.aspx?ArticleId=25532 |url-status=live }}</ref>