Conversión de formatos de DVD.

TECHNOLOGY Circuits, Basic

A Laboratory Tool Kit for Converting DVD Movies By PETER WAYNER Published: June 28, 2007

Jim Nuttle

WHEN Eric Petit wants to watch a movie on his PlayStation Portable, he pops a DVD into his computer and fires up HandBrake, a program he wrote for converting digital video files to fit onto his pocket-size game player. In a few minutes, the movie is resized to fit on the smaller screen where it can be watched without the plastic disc. HandBrake is just one of a number of popular tools that convert video files into a different format. Format conversions are becoming more common for people who want to watch movies through some means other than the television anchored in the living room. Anyone who wants to watch a show on a cellphone, a game machine or a portable media player like the Archos must become familiar with the alphabet soup of different formats and the software that manages them. Mr. Petit works with a team of volunteers from around the world who help him add new features to the program that he gives away (handbrake.m0k.org), but a number of commercial software companies sell programs that do the same thing. A quick Web search for "video conversion" can lead to dozens of versions from different companies. Techspansion, for instance, sells VisualHub, a tool for converting videos from sites like YouTube. There are dozens of similar tools, many sharing the same open source core written by some of the same volunteers who helped Mr. Petit write HandBrake. (As always, though, be wary of downloading any such software because it could contain viruses or malware.) The conversion software is relatively easy to use, converting films with a click or two. But they force video fans to deal with confusing names and abbreviations like DivX, MPEG, FLV and Ogg Vorbis. Users must learn to make decisions about technical matters like size of files, the aspect ratio and a dozen other options obscured by a cloud of mathematics. If the technical questions are complicated, the legal environment is even more confusing and uncertain because some think that making copies of your own DVD files might run afoul of laws designed to stop pirating. In 2001, Universal City Studios won a lawsuit against Eric C. Corley, the editor of 2600 magazine, for distributing DeCSS, a tool that would strip away CSS, the encryption layer that protects video on DVDs. Some argue that the decision makes tools like HandBrake illegal if they are used to convert video from protected DVDs. Wendy Seltzer, a lawyer working with the advocacy group Electronic Frontier Foundation, says that neither Congress nor the courts have done much to clarify the law. The Library of Congress, which has some responsibility for interpreting the law and deciding exemptions, has offered some help for film professors, but Ms. Seltzer says that doesn't help the average person. The software makers say there is a tradition of consumers being allowed to make personal copies of movies and music they own as a backup or to work on new kinds of equipment. For instance, people once routinely made tapes of their LPs. Laptop owners may choose to convert a DVD they own into files stored on the hard disk to avoid carrying the discs. Parents might want to convert a DVD collection into files stored on a hard drive, not only to keep sticky little fingers off DVDs but also to control access to inappropriate content. The legal issues have yet to be sorted out, and the technological one are nearly as knotty. But there is some vocabulary that needs to be learned by the growing number of people who choose to rip a movie for personal enjoyment: bit rate, codec, dimensions and frame rate. The prime consideration, at least for people who don't have several terabytes of storage in their homes, is whether to store a movie in as little space as possible. The bit rate offers the user a way to determine the final quality of the movie by controlling how big the file grows for each minute of video converted. Choosing the right bit rate can be tricky: the user tries to go lower and lower to save file space until the image quality is unbearable. Higher bit rates mean better-quality images with smoother transitions and fewer visual glitches around the edges of objects. The effects of the bit rate setting depend on the choice of the codec, the algorithmic software responsible for converting the data. Some of the most common codecs implement standards with names like MPEG2, or its later cousin MPEG4, or DivX. The newer algorithms tend to do a better job overall with lower bit rates, producing smaller files with fewer pixelated edges. The simplest way to shrink the files is to reduce the resolution of the video to the size of the playback screen. The size of the file depends upon the number of pixels in an image, and this is calculated by multiplying the length by the width. An iPod screen has a grid of 320 pixels by 240 pixels — a quarter of the pixels in a more standard 640 by 480 monitor display. Reducing the frame rate from a standard 30 frames a second to 15 frames a second can also slice a file, but it will make the image more jumpy. These solutions do not always offer simple reductions because of the mathematics of the compression algorithms and the way that they use a mathematical shorthand to reduce repeated blocks of pixels. Cutting the frame rate in half also reduces the repetition and the opportunities for using shorthand to compress the file. There are many other opportunities for confusion. Separate codecs convert the audio signal. MP3, for instance, refers to the audio part of the MPEG3 algorithm. The audio portion is popular for converting music, but the video part is largely supplanted by the newer MPEG4. So it is not uncommon to use MPEG4 compression for the video and MPEG3 for the audio. Computers that run on Windows and Macintosh software come with built-in tools (Media Player and Quicktime, respectively), but there are a number of other tools that might be more useful. VLC (videolan.org) works on most major PCs and other equipment and plays a surprising number of formats. The Core Pocket Media Player (TCPMP) is used by many Palm owners, and the development team is building a commercial product at CoreCodec.com. In most cases, the devices support the major standards, but there are always surprises. The MPEG4 files I that created played easily on a Philips DCP750 but played without sound on my Palm TX. I discovered that the playback software I used on the TX did not support the AAC audio codec that the hand-held uses. After converting the video to the Ogg Vorbis audio format by using HandBrake, I could listen and watch. You will have to experiment. But take solace in knowing that all this effort could become as passé as dubbing to a cassette tape. Steve Perlman, the chief executive of the San Francisco media and technology incubator, the Rearden Companies, thinks that the technical snafus and the legal debate will disappear when the average household gets a much faster Internet connection that can download movies in real time. "While adults may listen to music tracks hundreds of times, they are unlikely to watch movies more than once or twice, so there is little point in storing movies," he said. "You might as well watch movies live as they stream from the Internet."

Copyright by the New York Times 2007