You have completed your authoring project down to the last painstaking detail and you are now ready to send it to a replication facility to have discs pressed. No part of the Blu-ray authoring process causes as much concern and confusion as this final, all-important step. We asked Eclipse Data Technologies, one of the leading suppliers of verification and replication systems, to contribute this wiki-paper which details what a replication facility will do to your image and exactly how the image is processed to become a playable Blu-ray Disc.
Typical replication process with quality checks
(click image to enlarge)
Delivering the Master:
The first thing that you must address is getting the BDMCF image to the replication facility. For some, this will be done by Electronic File Transfer (EFT) on a high speed network. In reality, although this method is fast and reliable, it is generally cost prohibitive to obtain the bandwidth required to efficiently transfer 25GB and 50GB images. Therefore, the majority of non-Hollywood titles will need to be delivered on some type of physical media. There are two choices that can be considered:
1. Removable Hard Disk Drive: Removable USB 2.0 hard drives are accepted by most replication facilities. For the typical independent BD producer, this is probably the most common format for submitting masters. Make sure your file system is compatible with the replicator’s equipment. This typically means an NTFS or FAT 32 file system supported by Windows. Apple TM MacintoshTM users should be careful to avoid sending in an HFS formatted hard drive, as the replication equipment likely does not support Macintosh. If you can control it, an NTFS hard disk in a USB 2.0 enclosure is the delivery format most widely accepted.
2. CMF image on BD-R: As BD-Recordable drives and media become less expensive and more reliable, it will become feasible to record your CMF image to BD-R media for delivery to the replication facility. Not every replicator supports this workflow at this time, but BD-R might be a viable alternative to hard disk drives for some projects. One concern with this method is that the capacity of BD recordable media is slightly less than the pre-recorded media. This means a full Blu-ray image might not fit on a BD-R. For single layer projects it is possible to use BD-50 recordable media to fit the image, but full BD-50 projects will probably need to be sent on hard disk. If your replicator supports it, and your project will fit, BD-R may be an affordable and efficient method for delivering the master.
Incoming Inspection:
One of the first things that a replicator must do when they receive a master is to make sure that the image complies with a multitude of specifications. This includes the BDCMF specification, the AACS specification, and the Blu-ray disc specifications part I, II, and III. This step is critical because processing a Blu-ray title is time consuming and expensive. If the image does not comply with all specifications, then valuable time and money will be wasted. Replicators address this by inspecting incoming images with analysis tools. Virtually all replicators use EclipseSuite for this step. The EclipseSuite Blu-ray software contains a robust analysis engine with over 1000 rules that detect and report non-compliance in the BDCMF files, the AACS structure, the UDF file system, the BD-Java and BD-Live implementation, and even in the MPEG transport stream encoding.
In addition to inspecting the format of the incoming data, the replicator should also validate the integrity of the master. Data integrity checks ensure the data in the image has not become corrupted since the image was created. Eclipse has long offered data integrity protection solutions for CD and DVD formats using proprietary checksum technology. The Blu-ray working groups saw this as an advantageous solution and adopted a data integrity layer directly into the BDCMF. This means that all BD images should be created with SHA-1 integrity values stored in the BDCMF. These values allow the replicators to validate the data in the BDCMF. If the SHA-1 values contained in the BDCMF do not match the values calculated across the data, the replicator will halt the image processing as the data in the image is suspect. The SHA-1 values are a standard and should be adopted by all authoring systems and your replicator’s equipment should be able to test the validity of the SHA-1 values.
Another method for validating the integrity of an incoming image is the Eclipse ImageSignature. An authoring studio using Eclipse tools can create a compact Signature which acts as a type of fingerprint for the image. This Signature value can be recomputed at any stage of the process to prove that an image has not been corrupted. The Signature can also be used as a unique identifier of a title which helps track an image through the process and prevent mix-ups. An example is when last minute changes to a title require that a new image supersede an image that has already been submitted to replication. ImageSignature will ensure that the correct image can be easily identified. It is this identification feature that makes the Eclipse ImageSignature a beneficial compliment to the SHA-1 values built into the BD process.
AACS Encryption:
Once an image has passed incoming inspection, it is ready for AACS encryption¹. When an image is delivered to the factory, the user data is unencrypted and there is no AACS information present in the image. An image in this state is called a Type A image and it is not ready to be mastered. Unlike DVD’s CSS encryption, which could be performed on-the-fly during glass mastering, AACS requires the encryption to be performed offline ahead of time. This is because each image needs to be digitally signed by the AACS Licensing Authority before it can be mastered, a process which can take up to 48 hours.
During the AACS encryption process, part of the AACS key information will be generated and the audio video stream (.m2ts) files will be encrypted according to specification. The Eclipse ImageCopy encryption software performs these functions and then does an optional bit-for-bit verification of the encrypted data to your original source.
The encryption system will also calculate hash values of the encrypted data to fill in the content hash tables which are stored in the AACS content certificate. These hash values and hash tables link the AACS digital signature to the content on the disc and must be calculated and recorded in the content certificate that will be submitted to AACSLA for signing.
An image in this state is a Type B image. It has encrypted contents, a title key, and an unsigned content certificate with valid hash values.
AACS Signing:
The replicator is now ready to submit the unsigned content certificate, along with the required fees, to the AACS Licensing Authority. AACS LA will digitally sign the content certificate and return it to the replicator along with the current content revocation list (CRL). The replication facility then applies the signed content certificate to the image by embedding the content certificate file and CRL file into the proper location in the CMF image. Additional Media Key Block (MKB) information is also added to the image at this stage. The image is now called a Type C image. You image is now ready for mastering. It has encrypted contents, complete AACS key information, and a signed content certificate.
Replication Image Interchange:
Sometimes images are moved between replication facilities. This might occur because of outsourcing or load balancing between replicators, and it may also occur if an independent mastering house makes a stamper and requires pre-processed AACS jobs. When an image is interchanged for these purposes, it is most common for the Type C image to be interchanged. This is acceptable when all parties are AACS licensees, but it does present some exposure to sensitive encryption data. A future version of BDCMF is going to support secure Type C images where vulnerable key data in the BDCMF image is encrypted. Although the specification will support encryption, the encryption implementation is left up to individual replicators and Blu-ray manufacturing tool developers. Eclipse is working with leading studios and replicators to create a friendly and simple solution for securing BDCMF images. The new secure Type C image will allow replicators to safeguard the data throughout the manufacturing process.
Mastering:
In glass mastering, the data contained in the BDCMF Type C image is recorded using a Laser Beam Recorder (LBR). Although several different LBR technologies are used to master Blu-ray, in simplest terms the process is similar to burning a disc. A laser is used to record the modulated user data to a blank substrate that has a light or heat sensitive coating on it. After recording, the substrate is chemically developed to remove the exposed areas leaving a combination of pits and lands which represent the encoded data. A thin layer of metal is then deposited on the surface of the glass, after which it is placed in a metal electroforming bath where a metal plating process creates a rigid metal stamper with your data. After polishing and punching the stamper, it is ready to be placed in a replication molding machine to make your discs.
In mastering, a ROM-Mark is also added to the glass master. The ROM-Mark is an additional layer of security that is incorporated into the AACS encryption system. The devices used to record the ROM-Mark are tightly controlled by a separate licensing group. Since all Blu-ray discs must contain a ROM-Mark to be playable it is very difficult to make an illegitimate disc as only licensed replication facilities have the required equipment.
QC:
The purpose of data verification is to make sure the data on the replicated Blu-ray disc is the same as your original master image. This data comparison is essential to confirm that the encryption and replication processes were done properly. Typically, after the first discs are made, a replication facility will take sample replicas and use a tool such as EclipseSuite ImageVerify to verify the information on the disc.
A comprehensive verification tool needs to decrypt the disc contents to compare against the original unencrypted user data. By performing this decryption, you can be assured that the entire AACS encryption and signing process was done correctly. If the keys, hash tables, or encryption are wrong, the verification will fail.
ImageVerify is a flexible verification tool that allows the replicator to verify a disc to the original source, the Type C image (where both images are decrypted), or to the Eclipse Signature, depending on the replicator’s process. If the image was submitted with a signature, the QC step can ensure that the disc was produced correctly and that the correct title and version were used. Whichever tool and method is used, data verification is the last step on the image’s journey through the replication process. Your discs will be tested for other characteristics such as error rates and reflectivity, and the surfaces of the disc will be scanned to detect defects in the surface and printing of the discs. Most replicators also do some basic type of playability testing in popular Blu-ray player models. If all tests pass, your discs will be on their way to you soon.
If you (the author) have a requirement or interest in the final QC of the title, a simple check of the replica signature ensures that the image got through the process correctly. Eclipse ImageAnalysis with the AACS option is a simple, cost effective tool for that purpose.
Conclusion:
You put a lot of time into creating your image. Choose a replicator that uses the best tools to process your image. While all tools are based on the same specifications, implementation is everything. Many points in the specification are ambiguous and subject to interpretation. Only experience and strong relationships in the industry will ensure the highest compatibility and minimum amount of problems. It is inevitable that some images will result in errors and warnings during the replication testing process. Your replicator should be able to explain the nature of any errors or warnings so that quick decisions can be made to resolve them. Hopefully your familiarity with the replication process will help you in those situations.
¹ The Eclipse ImageCopy software actually performs the incoming inspection and AACS encryption functions in a single integrated step. For clarity, each function was discussed as a separate step in this wiki-paper.
All trademarked terms used in this paper are the property of the respective trademark holder.
About Eclipse Data Technologies:
Eclipse is the leader in optical disc premastering and mastering products. Their rules-based analysis engine revolutionized testing in the optical disc industry and is used by virtually every disc replication plant in the world. For more information about Eclipse and its products, please visit their website at www.eclipsedata.com.
