Thomson has developed a new MPEG-4 AVC compression engine aimed at the production of HD-DVD and Blu-ray for the home movie market.
Working with the Thomson-owned Technicolor Labs, the Thomson corporate research labs in Princeton, NJ, created Tiger to be an exceptionally high quality video encoder for the HD optical disc formats that streamlines the process and delivers workflow efficiency.
HD Technology Update spoke with the general manager of the research labs, Jeffrey Cooper, to find out more about Tiger.
HD Technology Update: What are the primary strengths of the Thomson Tiger compression engine for MPEG-4 AVC?
Jeffrey Cooper: We focused on two main aspects for this tool. One was very high video quality to support HD-DVD and Blu-ray applications, and second was optimized workflow for the compression authoring service business.For optimization, we reached out to Technicolor for input, relying on their customer-side insights.
We created a special user interface that streamlined how Technicolor does their compression authoring work to make it more efficient.
HDTU: What aspects of the user interface make the process more streamlined than other encoding tools?
JC: Tiger has quite a few features that streamline and improve the encoding process. For example, it provides full thumbnails so you can navigate through the content. It allows scene-by-scene or even frame-by-frame re-encoding, with many parameters exposed to the compressionist. With these tools, compressionists can control a number of components of the frame coding process.
So, the customary workflow is, compressionists do an automatic encode, which for Tiger is a multipass process, and then they do a quality analysis viewing. Typically, they note an item here or there. What we've done enables compressionists to go back in and very quickly identify those frames that need to be modified. The advanced user interface, including the video player, is used interactively with the content to modify parameters and then perform the re-encode. In fact, compressionists can even start re-encoding some scenes before the whole quality analysis is done.
There are a lot of other features like that, which enable encoding to be more efficient and provide the compressionist with more control. There is the ability to categorize scenes depending on the content type and to notate where the scene changes are.
The encoder has a lot of smarts on its own,such as detecting scene changes and fades, but the compressionist also has those tools and they enable him to further perfect the encoding process.
HDTU: How efficient is Tiger in terms of compression?
JC: It's very efficient, we believe. Again, it's aimed at the very high quality — what we call transparent video quality — for HD-DVD and Blu-ray. The bit rates there tend to be in the teens. We've run Tiger down to 10Mb/s for these applications and achieved very good quality, transparent quality. So, we think it's definitely met its requirements.
HDTU: What strategies have been employed to assure maximum efficiency and accuracy in encoding?
JC: Any encoder of this nature has to be compliant and testing it for compliancy has been a major part of our work. There are two aspects of compliancy: H.264 compliancy and compliancy with HD-DVD and Blu-ray.
We've used several approaches and testing methods. On H.264, we've been verifying our bit streams against what I describe as golden decoders — actually several. For both H.264 and next-generation DVD formats, there are verification tools available in the industry from several different parties, and our streams go through those. Then finally, they get burned to some test discs, which are played on all the devices in the industry that are available.
So, it's been quite a big effort to make sure Tiger is compliant, and I really believe we have perhaps one of the most compliant encoders in the industry right now. High definition is still a pretty young DVD format. It's just emerging, so there's been a lot of effort to make sure the Tiger bit streams are compliant to the new standards.
HDTU: Can you discuss what strategies or technologies are being used to address anomalies that arise during difficult scene changes like those with lots of motion answer?
JC: Tiger includes what we call a preprocessor before the encoder. What that preprocessor does is examine video content and characterize the types of video frames to be encoded. I have already mentioned things like citing where scene changes or fades are very important for the encoder to know.
There are a lot of things we look for. We look for motion as you mentioned. We make sure we are aware of, if you will, the true motion that is in the picture. We look for dissolves, which is a type of fade that mixes two different scenes and can cause the encoder a lot of problems. We make sure we are notifying the encoder of where those things are.
There’s typically noise and film grain in the image, and the film grain needs to be identified and preserved. We look for the film grain, and we apply the correct encoding strategy to preserve it. There are a lot of varieties in the grain types.
Banding is another thing we look for, especially in animated content or content that has some CG in it. At one point or another through the compression process, banding can occur. So, we have some debanding strategies within the encoder itself. There has been a pretty major effort to make sure we address banding issues.
Those are some examples, but there are some other things we look for that provide inputs to the encoder for rate control and things like that. So, overall a pretty big piece of Tiger’s encoding process is the work done in preprocessing.
The actual AVC encoder is a multipass encoder. In addition to preprocessing, it goes through multiple passes. During those passes, there is some evaluation of the quality within the encoder and it works to improve the video quality in difficult areas. The encoder has quite a bit of intelligence already, and once it goes through all of that, the compressionist can still go back and tweak things further.
HDTU: When the preprocessor identifies, for instance a dissolve, what does it do?
JC: There are tools within AVC that can be specifically leveraged for things like dissolves or fades. There is a tool called weighted prediction, which is one of several technology contributions to AVC by Thomson.
Basically, what we do is try to use weighted prediction and other tools of AVC to encode fades, dissolves and other scene transitions as efficiently as possible. The way weighted prediction works is essentially it allows you to add a kind of an alpha blend to the reference frames, and as you can imagine for a dissolve, it can then get very good performance from a compression perspective.
HDTU: Will MPEG-4 AVC remain primarily targeted at distribution and transmission, or do you believe it will have a role in the production chain from acquisition, perhaps ENG, to post production?
JC: I think we're seeing some interest in the industry for acquisition and post within with the MPEG standards body right now. There are some profiles still being finalized for intra-only support and 4:2:2 and 4:4:4.
Of course, MPEG 4-AVC already supports very high bit depths, so the standard is certainly capable. I see some movement in the industry. There are some prosumer cameras coming to market. There’s certainly potential for this format to be used for acquisition and post, but those applications are still not firmly entrenched.
HDTU: How will Tiger begin showing up in the marketplace?
JC: Today, it's been deployed within Thompson's Technicolor division. It’s being used there for productions that are moving into the manufacturing stage. I can’t give you any title names at this point, but they will be coming to market within the next few months.
Right now, Thomson is exploring some exciting opportunities for Tiger outside of Thomson, but at this point I have no announcements I can make.
HDTU: Is there anything you’d like to add?
JC: We’re very proud of the tool. I think one of the nice things about developing this tool was leveraging the two synergies within Thomson, that is Technicolor system knowledge, if you will, in this area and Thomson's compression expertise. They really came together to make quite a powerful tool.
We’re just excited to see it being used to create titles for consumers to enjoy. I think we've moved the bar up a little bit in terms of video quality for H.264 and for consumers.
Tell us what you think!
HDTU invites response from our readers. Please submit your comments to firstname.lastname@example.org. We'll follow up with your comments in an upcoming issue.