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Monday, January 23, 2006
Making Professional DVD from Authoring to Replication

8. Common DVD Authoring Mistakes

4.0 Common DVD Authoring Mistakes

As a DVD replicator we have received over thousands of DVD masters from our clients. It is our pre-mastering QC's job to check the masters for errors and compatibility. To our surprise, more and more DVD masters have problems in some form or other. Let's briefly list the commonly seen problems here in a hope that you will not commit the same mistake when you make your DVD for replication.

4.1 Not enough space between IFOs and BUPs.

Nero, being the most popular disc burning software on the market, has its Achilles' heel. When you use Nero to burn an ISO file, NERO will try to help you conserve space by packing all the files tightly and disobey the original ISO layout. The consequence of this is: The CRC Error Protection designed for DVD might be broken.

How could this happen! To understand why we need to know a little bit about the structure of a DVD. Normally within the VIDEO_TS folder you will see the VOB files are sandwiched between the IFO and BUF files. The IFO files contain the pointer information, more or less like the table of contents for a book. The VOB file is the actual content, and the BUP file is a backup copy of the IFO. Without the IFO file the a DVD player would not know where to start and where to end. If the IFO file is damaged, the DVD player will try to look for the playing direction from the BUP file. Unless both the IFO and the BUP files are damaged then the DVD is doomed.

Most reputable DVD authoring software will try to leave a gap between the IFO file and the BUP file when the VOB file is too small. But Nero will break this layout by squeezing all the files together. If this happens, your disc will still play without any problems until some day the area contain the IFO file is scratched or damaged. DVD players will try to recover the damaged data from the backup sector, i.e the .BUF file. But if there is no enough space separating between the IFO and the BUF file, chances are the same scratch that damages the IFO sectors also damages the BUP sectors rendering the DVD totally useless.

The solutions to this is to re-create your DVD with the proper gap. If you DVD have menus chances are the VOB files are big enough and you won't need to do anything. But if your DVD is the simplest kind with a video playing from the beginning to the end, then you should do some patch work. The article here will be your solution.

4.2 Try to create a copy protected DVD-R

A commonn misconception is that when you author your DVD with the copy protection flags enabled, then you can burn a copy protected DVD-R. The fact is there is no copy protected DVD-R. Copy protected DVD can only occur on pressed DVD, i.e. the DVD discs that are manufactured from a glass stamper. That's the main reason why replicators will need you to provide DLT tapes instead of DVD-R as master when you request to have copy protection.

The reason behind this is copy protection information is written only on certain track of a DVD. As member of the DVD Forum all DVD equipment manufacturers are bound by the rules so DVD burners cannot write such information on a DVD-R. If you are a firmware guru you might be tempted to think you can hack the firmware code so the writer can record copy protection information. Although I cannot be 100% sure, DVD-R manufacturers might also be bound by the rules not to have the copy protection track writable.

4.3 Didn't test playability on enough number of players

DVD technology, though a decade old, is still not mature to the point that there is a universal compatibility. To create a DVD that will work on all DVD players is really a myth. If you can get your DVD work on 90~95% of the players than you are in pretty good shape. The incompatibility comes from the fact that DVD players has evolved and there are old DVD players and new DVD players. There are also DVD players stick to the DVD specifications tightly and there are DVD players that are more tolerant to error.

If you don't have a matrix of DVD players then you won't have the assurance. A DVD plays well on your own DVD player does not mean it will play on other people's DVD players. That's why it's crucial to hire a reputable replicator who will test your master on different mix of DVD players. New Cyberian Systems, Inc. will test our clients' DVD master on about 20 brands such as Apex, Pioneer, Samsung, Sony, Toshiba, etc. The brands we choose represent a good market distribution that covers from high-end to low-end players.

4.4 Use cheap DVD-R as master

DVD-Rs are made all the same, after all they are all digital and either they work or they don't, right? If you believe in that then you are dead wrong. Cheap DVD-Rs, I mean in terms of quality, have plagued the market. When you burn a DVD-R with NERO and congratulated with the "Successful" dialog, you usually have the comfort of mind that the burning is truly successfully. After reading this, think again!

There are only a few DVD recordable media manufacturers in the world. The brand name DVD±Rs you buy from a physical or online store are mostly likely not manufactured by the brand owner. For example, DVD±Rs carry the name of HP could be manufactured by a Taiwanese company called CMC. Ritek, another recordable media giant, turns out ultra good quality discs (so called grade A) and some craps (so called grade C).

If you only need to duplicate few DVDs for friends and families, then getting the cheap DVDs won't do you too much harm. The worse case is you just burn the DVDs into coasters and burn a little bit of your time and money. But when it comes to high quantity replication, you'd better be picky on the DVD-R media. Bad DVD master will result in many quality related issues such as skipping, freezing, and blockiness.

Good DVD-R brands include: Apple, Fuji, Maxell, Sony, Taiyo Yuden, and TDK. Try to avoid Imation, HP, Kodak, Philips, Princo, and Radius. But don't just take my word for it. Always find out the Media ID of the media you just bought by using tools such as DVDInfo/DVDInfoPro. The tool will tell you who's the true manufacturer behind.

You should also test your media with NERO CD-DVD Speed.

4.5 Mis-handling of DVD

Scratches and finger prints on the data side of a DVD are absolutely No-No's for glass mastering. Very often people damage the DVD surface without even knowing it. Believe it or not, the plastic on the DVD surface is actually very soft. If you put a DVD and rub it on a table top softly, it won't need hard examination for you to see scratches are already all over. Although DVDs are designed to have error correction, too many errors will slow down the decoding. From the mastering point of view, too many scratches will reduce the reliability of the stamper. To avoid a "garbage in garbage out" situation, you should

  • Never put a DVD on a table without proper protection
  • Never touch the DVD surface with your fingers. Always handle a DVD with the thumb on the rim and another finger through hole at the center hub. If you find fingerprints on the DVD surface, clean them with a damped tissue or a alcohol cotton swab.

4 6 Didn't enable verify when burning the DVD-R

Disc burning software programs usually have the "Verify" function. For example, Nero Express has the "Verify data on disc after burning" checkbox at the final stage of the wizard before you hit the [Burn] button. If you find such feature, check it! This is a very economical way to have a final sanity check. In our daily routine of duplicating thousands of discs everyday, we have found many instances of successful burn but fail the verification. The failure can be caused by many unforeseeable reasons such as voltage fluctuation or dirt on the laser head.

4.7 Send only one master copy to your replicator

When you send your master to a replicator, it's always good idea to send two copies. Why? The master you send out will go through a long journey and be passed along many hands. The stamping machine at the US Post Office, the guy throwing parcels at the FedEx hub, the conveyer belt at the UPS sorting facility all can contribute to damage your DVD master. Once again, in our experience in receiving thousands of masters from our clients, we have found very often the masters are damaged or useless for other reasons. If we don't have a backup copy to work with, all we can do is to call the clients and ask to send us the master again. You not only waste money on the shipping, but also delay your deadline. Just as an insurance, always send two or more copies to your replicator; especially when your project is mission critical.

4.8 Did not include a PCM or AC-3 audio track for NTSC video

NTSC DVD allows to have 8 audio tracks. Audio formats supported by the DVD specifications are AC3 and PCM. Many DVD players also support the MPEG-I Layer II format, especially those cheap DVD players that are meant for the Asian market to support VCD and SVCD. These DVD players have now entered the US market and

4.9 Set a bad layer break for DVD-9

Remember DVD-9 is a single-side dual-layer format?  The DVD layer break is the place where a dual layer DVD switches from the first layer (layer 0) to the second layer (layer 1). DVDs are laid out in sectors with each sector contains 2048 bytes of content. The first sector of a DVD is sector 0; the second sector is sector 1, ......... the nth sector is sector (n-1).  This way, the first sector of layer 1 is actually the number of sectors on layer 0.

Ideally you should set the layer break point near the middle of the video with layer 0 slightly longer than layer 1.  To understand this we need to know how the play head in a DVD player travels.  Starting from sector 0 on layer 0, the play head will travel away from the center until it reaches the break point.  Once passed the break point the play head will switch to layer 1 and travels back towards the center of the disc.  With this in mind you will understand why you cannot set layer 0 smaller than layer 1 because doing so layer 1 won't have enough space. 

Theoretically you can set the break point with layer 0 substantially longer than layer 1.  But this suffers from the disadvantage that layer 0 content will be written close to the outer radius of the disc.  DVD disc are read more reliably closer to the center.  Although you are unlikely to see any problems for new DVD players, old players might create problems such as skip or freeze.

Besides, the break point should occur at a sector number that is divisible by 16.  The reason for this is an ECC (Error Checking and Correction) block is formed for every 16 sectors.  If the break point is set at non-sixteen-divisible sector, an ECC block will be split by the layer break point.

If you DVD authoring software supports DVD-9 it should give you the advise where the break point should be set.  Make sure to read the User's Guide that comes with your software to set the break point correctly and wisely.

4.10. Broken menu links

Menu links are like the hyperlinks on a web pages.  If configured incorrectly their behavior will be quite different from what you have expected. Common problems are

  • Link to the wrong clip
  • Link to nowhere; meaning no effect on clicking
  • Link to non-existing clips; same as the page not found on web pages

4.11. Menu text cropped

Most DVD authors assume a computer screen is same as a TV screen. In reality, the TV screen border is thicker than what you might have thought.  Very often we receive masters from our clients that play perfectly on a computer but the menu text got cropped when played with a set-top DVD player on TV.  So when you author your menu, always keep in mind that the visible area between a computer monitor not the same as a TV screen.  Good authoring software normally will provide a suggested safe-zone and you'd better follow the suggestion to avoid your menu texts disappear or half-cut on a TV screen.

4.12 Hard code drive letter for enhanced DVD, i.e. DVD with video and data

An enhanced DVD is a DVD with both video and data sessions.  The intention is to make the DVD viewable on both set-top DVD players and computers. A common problem we found on enhanced DVD is that the video works perfectly on set-top DVD players but fail on some computers.  One obvious problem is that the author fails to see that every computer in the world is more or less different. A program works on computer A doesn't mean it will work on computer B.  Hard code drive letter is the #1 crime in computer programming. A DVD-ROM drive called D: one my computer doesn't mean it will be called the same on other computers.  If you hard code the drive letter, your DVD will fail on other computer systems that don't have the same drive letter as yours. We had clients yelled to the hell that their DVDs were OK.  But when asked to test on other systems other than the authoring unit, they immediately saw the problem.  So do test your DVD thoroughly on different systems before signing it off to a replicator.  

4.13 Audio and video out of sync

The causes of AV out-of-sync are manifold.   They can occur during capturing, editing, compressing, and rendering.  With the ever increasing computation power of an average PC A/V out-of-sync is becoming less a problem, albeit still found in many DVD masters that were sent to us.  Studies showed we human can tolerate audio lagging video more than audio leading video. The A/V out-of-sync acceptability thresholds are 185 ms for audio lagging video and 90 ms for audio leading video.

Common causes of AV out-of-sync are:

  • Drop-frame is the number one culprit for AV out-of-sync.  Drop-frame occurs when the computer is not fast enough to process the video and audio stream.  You can minimize the occurrence of drop-frame by having computer with powerful CPU, a hard drive with high spinning speed and seek-time, and you should optimize the performance of your hard drive by defragmenting it from time to time.
  • Choose the mismatched attributes for source audio and capturing settings.  For example, if the DV audio is set at 12-bit 32KHz and you choose the 48KHz project setting for capturing, AV out-of-sync is likely to occur.
  • Do not use the hardware profile for capturing.  Good capturing software usually have a set of hardware profile for you to match your device.  If your device is not in the list you can only choose the generic profile.  Doing so will leave a lot of guess work for the software.  For example, the audio frequency of certain brands of camcorders might not be truly 48KHz but 48.0005KHz.  Without the hardware profile to compensate this discrepancy the captured audio will have many sample cycles less then the source audio; 5 x 3600 = 18,000 cycles to be exact in one hour.

A good way to check whether AV out-of-sync occurs is to demux the audio and the video, i.e. separating them as two individual files.  Play each file in any compatible players (such as Windows Media Player) and then observe their lengths.  If the lengths differ than there is AV out-of-sync for sure.

4.14 Subtitle out of sync

This is purely a careless mistake with crappy quality control.   We point it out here just for you to add this as your checklist.  Since you know your own DVD better than anyone else in the world, only you know the answer where and how to fix it.  Word of advise: The same old hackneyed cliche - Test the DVD thoroughly before signing it off to the replicator.

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