The quest for Quality

As filmmaker you have full control over the quality of your production, but how can you ensure quality during the DVD production and replication process for your film, game or software? ROBERT BARNES, Vice President of Services at AudioDev, explains how you should get involved.

DVD is a powerful format to bring creative content to audiences. It supports multiple video streams, audio streams, and subtitle streams, which are all synchronized to the video content. DVD allows room for extra content, including software and games, and can be packaged in visually attractive ways. It can be produced for a reasonable cost per piece, literally pennies, for a variety of geographic markets.

Finally, high quality discs can expect to last for many years to come. Yet there are challenges to putting a 9,4 GB of data on a piece of plastic that is 120 mm wide and a maximum of 1,5 mm thick. And these challenges can affect the viewer experience.

QUALITY CHALLENGES

What are the common problems a viewer can experience when trying to access contents from a DVD?

Stuttering

Stuttering describes the situation when a scene on the DVD freezes up during viewing. It occurs when there is no data flow, in other words the laser does not find the next set of data that it should read. For instance, when there should be a layer transition, stuttering would occur if the data buffer runs out before the layer transition has been executed. You might also experience stuttering if something on the disc surface forces the laser to move back one track (ex. scratching, matrice bump).

Poor layer transition

DVDs are actually made up of two layers, and content is recorded on both. In some cases there could be poor transition when the player moves from one layer to another causing frozen frames. As seen above, the capacity of a buffer at the end of one layer could be exceeded before the transition takes place. But other problems might originated with the content produced on the disc. In an extreme case, the content might have been recorded on one wrong layer. This is generally a problem that occur in the disc replication process. But it could also be the result of errors when the content is placed on the stamper during the mastering process.

Skipped video streams

In some cases video streams will be skipped completely. For instance, an entire scene might not be present when the DVD is played back on some older DVD systems. This can happen if the authoring tools used are more advanced than the player systems used to interpret it. To illustrate with an example: When the authoring house viewed the film on their system the scene was present, but when it was transfers to a disc and played on what might have been an older drive, the scene may not be able to be viewed.

Pixelization

Pixelization happens when the video signal splits into its component parts. A mosaic pattern appears on the video screen. This is caused by an uncorrectable error in the data stream at any point on the disc. Pixelization is most likely traced to errors in disc manufacturing; these are not software errors.

Menu system failures

There are situation where menu icons or pointers may activate the wrong spot on the disc, or may not be active and move the viewer to the desired content. The most irritating menu failures happen when a viewer ends up in a place on the disc and cannot go back. In such a case, the only solution for the viewer is to eject the disc and start again. Similarly, the software may not be properly set up to skip through content. These failures are nearly always due to a problem related to the authoring process.

Disc/Drive incompatibility

A disc may not work properly on a specific model or make of drive. This is perhaps one of the biggest uncertainties in releasing DVD content. A drive consists of optics and software, and these parts are developed to be optimised to the specifications for DVD-Video and DVD-ROM. The interaction between disc and drive has as much (or more) to do with the software controlling the drive as the optics. But both play a role. The closer to specification targets a disc is manufactured, the wider the range of drives that will be supported – there will be wider tolerance in playing properly. A disc within specification limits will be highly likely to play in any drive, though this is not 100% certain. Discs closer to or over the limits may fail to play properly in some drives. These failures usually can be traced to the actual disc production.

QUALITY CONTROL & ASSURANCE PROCESSES

The above considerations illustrate that the problems an end user can experience have little to do with the actual nature of the content on the disc. Very little of what could be classified as a poor quality disc, is in fact due to problems caused by the filmmaker – yet they affect very much what the filmmaker is trying to achieve.

There are a number of different tests that ought to take place during the production process to control that these and other problems will not occur. There are four main areas of quality control and assurance testing.

Content verification

Between the original data that are produced in the creative stage of production and the manufacturing and packaging of the finished disc, there are a number of processes where the content might be left out, damaged or even destroyed. There is a risk that data is not transferred correctly in the production process. Bit-to-bit testing can be conducted to ensure that the contents on the master have been fully transferred onto the disc. Test systems made by companies like Eclipse and DCA perform this type of testing.

Physical & electrical properties testing

A significant form of testing ensures that the physical and electrical quality parameters set out in the industry standards for DVD production have been met. Tests should be conducted by disc manufacturers at the end of the production process with equipment like the AudioDev CATS tester to ensure that the disc is manufactured within the prescribed DVD format specifications.

The tests are most often performed at actual playing speed and cover the whole disc. The target standards are described in the DVD Forum specifications for DVD-Video and DVD-ROM format like films and games, as well as in the European Computer Manufacturing Association Specifications (ECMA 267). Discs that are manufactured within specification limits will have extremely high likelihood of playing on all drives.

There are also physical tests conducted during the production process which quickly scan some basic parameters like reflectivity and birefringence. These tests are done within seconds in the production line. They are not thorough, so in-line testing needs to be backed-up by off-line testing. Dr. Schenk and Basler are two companies making equipment for in-line physical testing.

Linear playback testing

Linear playback testing checks all aspect around the functioning of the disc including the menus, audio and subtitle streams, the functioning of added content, scene selection, scrolling, the total functioning of the disc. This type of testing is usually conducted at an early stage of production with a so-called ‘check disc.’ Often this testing is outsourced to an external quality assurance lab by the production facility.

Drive compatibility testing

Testing can be carried out to see how the disc will function in different DVD drives. Discs that are manufactured within specification limits should not have difficulty playing on different drives, but simple tests can be conducted to see how the disc functions on different hardware. Such testing can usually reveal to a high degree of accuracy the percentage of drives in the market on which the disc will encounter difficulties or fail to play.

STEPS YOU CAN TAKE

While the production process remains outside the hands of film-makers, there are some steps which can help ensure a quality viewing experience. Set your own quality programme, which can be as simple as setting the quality targets that you expect your suppliers to meet.

Select

Care to ensure that you choose a quality disc manufacturer that has a reasonably dimensioned quality control programme within its facility, and that it has enough testing equipment to meet production needs. Ensure that the company can and will meet your quality targets.

Inspect

Ask your disc manufacturer to give you copies of the test protocols from the production runs. It is a simple way for you to see that parameters are within specification. As a rule of thumb one discs per 3000 unit produced should be tested on equipment like the CATS reference tester. This is a generally-accepted testing frequency. If your film is being replicated in smaller batches, then one test at the beginning and one at the end should be conducted. The CATS test protocol is a de facto industry standard and provides, in effect, a way for professionals in disc production to speak to each other and understand quality between different production batches and facilities.

Control

Test some samples of your finished product with an independent testing facility like AudioDev’sTestCenter. Independent testing helps ensure that when your discs is placed in a drive it will play as you and your customer expect. A third-party check helps you to do more than simply rely on the word of your disc manufacturer that quality controls have been performed. Your disc manufacturer, while probably committed to quality, will of course have different motivators and drivers affecting how they implement quality control in their manufacturing process. With your own control, you can be sure that your DVD is being produced in a high quality fashion.

SECURITY

A quality production process involves authoring, mastering, quality testing, replication, printing, packaging and distribution. There are number of players in the chain. Quality is only important as long as your content is protected. You need to ensure that your partners in production take adequate care of security, so that your intellectual property does not fall outside your control.

CONCLUSION

Its is easy to dismiss optical media as a piece of cheap plastic, but when you think of all the work you put into the content, the value is much more than the disc manufacturing costs. Your artwork is worth more than just a few pennies, and it ultimately costs so little to ensure that it will be transferred to the end-viewer in a high quality way.

Quality control represents only a very small part of the overall creation and production budget. And a good quality control throughout the production process will minimize costs of returns for you and your distribution channels.

Quality control and assurance is ultimately up to you – the filmmaker. Awareness, knowledge and actions to control the process as described in this article will help you be sure that your work is a quality production all the way to the end-user.
...

Article Comments

comments powered by Disqus