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ratDVD - A New Way to Compress your DVD Collection
June 14, 2005
Thomas Mennecke
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XviD technology is a blessing to the file-sharing world. It allows the individual to compress a large video file into a manageable size. Many XviDs existing online were full length DVDs in their former life, but have been compressed to the size of a CD for the convenience of the end user.

While this XviDs are impressive, it is difficult to include other characteristics of DVDs that have helped make this technology popular. This includes menus, language support, subtitles, special features, director's cuts, trailers and other extras. Almost exclusively, these additional features are cut out of XviDs to make the final product as small as possible.

ratDVD hopes to change that, but not necessarily be a replacement for XviD.

ratDVD is a new format that can take your DVD9 or DVD5 and compress it to 1.5 gigabytes or less. In addition, while using most compression technologies means loosing extra features, this is not the case with ratDVD. Despite the high compression, all additional features accompanying the original DVD will remain with virtually no noticeable loss in picture quality.

Although ratDVD is a significant advancement, XviD still has some advantage when it comes to portability. Since XviD is compliant with the MPEG-4 standard, XviD discs will play in stand-alone DVD players that support the DivX format.

ratDVD is not intended to be used this way - at least not directly. It is a technology that allows the individual to play, compress, back up and catalog their DVD collection via the hard drive. The cataloging and compression features appear to be its strength. Those who may find this tool useful are individuals with many DVD5 or DVD9 movies on their hard drive, have no intention of burning to disc and wish to save serious hard drive space.

In addition, the "tagging" feature of ratDVD allows the individual to properly identify the movie file through (Internet Movie Data Base.) Like a properly tagged MP3 file, this feature fills the ratDVD file with information such as the proper actor, genera and plot information. The tagging feature also displays the movie cover through Windows Explorer for easy navigation.

From a file-sharing perspective, ratDVD allows for quick transmittal of DVD movies at the cost of tasking the end user with converting the file back to its original format - a fairly reasonable trade-off for marginal broadband users.

To get a more technical perspective of ratDVD, Slyck spoke with “Splinter”, lead programmer of ratDVD.

1) What was your motivation behind developing this tool?

I like movies on DVD and for me what a DVD makes really different from VHS is most of all the nice stuff you can do on DVD.

Things like full anamorphic picture, seamless branching, 9 video angles, 32 subpictures, 8 audio channels, different movie versions (Directors Cut, Theatrical version, etc.), bonus features like making of, visual commentary and the complete menu system like for example title navigation became available with DVD. Some movies like Memento for example can only exist on DVD as you can change the order in which they are played back or have an interactive story.

Without ratDVD there is just no way to put all these features, the complete movie into a compressed format. So, currently when I look at what is available for download (and I mean this both for file sharing and official video on demand), this is purely linear video like VHS. It almost seems as DVDs with all their nice features wouldn't exist.

Maybe it's only the movie industry that sees the need to offer "something" online but cripples it in a way that people still need to buy the DVD to get the full stuff? Anyway, I did ratDVD to show that there is no technical reason for this. And I think that the market will tell what people want – and in the end the movie industry will have to follow what people want instead of forcing crippled video and DRM into each and every place.

2) What kind of research/development went into creating RatDVD?

It was work of nearly 2 years - sometimes day and night, sometimes nothing at all.

The video encoding part was relatively simple compared to the details that are needed to carry all the information to be able to reconstruct a feature complete DVD. For audio I just used existing filters so there was nothing to worry about.

Probably most of time was spent in testing. I'm glad I had some help in that – without these guys I couldn't have done it.

3) Explain how you are to compress a large DVD9 to a mere 1.5 gigs while still retaining the quality AND extras?

There is no magic. Modern video compression is just a lot more advanced than the MPEG2 which is used on DVDs. When you think about it, the MPEG2 standard was defined more than 10 years ago. Most concepts used therein are 15-20 years old.

ratDVD features many of the modern developments in video-encoding. One of the main goals behind MPEG2 was to keep the decoder relative simple in order for it to run well on the hardware of the day. ratDVD by far didn't meet such rigid design limitations and obviously research and development of video-encoding technology didn't stop with MPEG2. Many features of the video codec is just far beyond what MPEG2 has to offer. ratDVD's coding efficiency comes to a large extend from better prediction. In the ratDVD video codec a lot more complexity is added to various kinds of prediction. Say in MPEG2 the only intra prediction mode that you have is DC-prediction. ratDVD has more intra prediction modes to select from. Then of cause DVD GOP's are typically only about 15 frames, ratDVD allows far longer GOPs. When you compress video very much with MPEG2 you tend to get very visible block building in the picture – ratDVD and other modern codecs has deblocking filters which basically blurs around the edge of such a block and blur tends to be far less eyecatching than blocks. There is no one trick, it's the sum of many small improvements that end up making an huge difference.

Another important thing is that the audio gets (optionally) transcoded from AC-3 5.1 to AC-3 VS. The quality is still great but it saves also a few hundred MB on the average movie.

4) How would someone who's compression technology of choice is XviD take advantage of RatDVD? How is it useful to them? Are these two completely different animals that really cannot be compared?

With ratDVD the whole DVD with all it's features gets compressed. With XviD you loose all the special features and you can only compress one linear version of (typically) the main title. Things like multiple audio tracks, subtitles, etc. that are very important in most non-English native speaking countries are just a mouse click in ratDVD – but very hard to do with XviD. Then of cause you have the advantage of features like tagging where you can store information about the movie, like the DVD-cover, along with the movie. But I think best of all is that you are able to reconstruct the complete DVD from the ratDVD file – that makes it compatible with every player.

So in summary I would say that XviD is great if you don't have a DVD as source - e.g. it is my format of choice for TV rips or movies that are not yet available on DVD. But for everything from DVD I think that ratDVD is the better choice.

5) What are some of more signficant hurdles you are trying to overcome?

On the technical side besides many smaller improvements I want to optimize the quality and speed - but I would say that this is well under control.

I think the main hurdle to overcome is acceptance for ratDVD in the community. It would be my dream that once the movie industry sees a "full DVD" format like ratDVD to be successful, they will offer something equal by themselves. The music industry is just starting to understand now. Let's hope the movie industry is a bit more quick.

6) What additional features can we anticipate?

Well, I am reading the forums and see very good ideas there. This ranges from small things like the ability to burn a DVD and shut down the system automatically after a convert to huge projects like porting to mobile phones/PDAs. I am currently collecting and prioritizing these requests so I can't really say.

Personally, I see some bug fixes for playback and optimizations regarding speed and quality as first priorities. But we'll see…

7) When will the source code be fully released?

I simply don't know. Currently I am releasing source for things that come up as I go and where I think that are most useful for people when they integrate ratDVD into their own programs. However, the focus of my development if clearly directed towards the next version and I am trying not to do too many other things that would distract me from this.

8) A few have moaned the conversion process takes quite a bit of time, will we see this improve?

Well, speed is relative. When you compare ratDVD with other encoders the first thing you have to note is that ratDVD actually encodes a lot more – very often on a movie of 2 hours comes bonus, menus, extras of another hour. Then the transcoding of the audio is another 5% in speed (in verage).

Overall, when you measure it, ratDVD is about half the speed of XviD and 2-3 times faster than H.264/WMV implementations. This is not that bad for a first version, especially since it additionally has to handle the DVD stuff that accounts alone for about 10% at a standard quality setting of about 100.

But can it improve? Yes, definitely. Otherwise that would have been the first release of an encoder that couldn't ;-)

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