Lenovo ThinkPad 770 DVD Information Brief - Page 4

lines and edges are preserved, resulting in high image quality. In simple terms, higher compression ratios can be applied to sequences depicting little or no change from frame to frame. Action sequences require more gentle compression. MPEG compresses each frame of video uniquely. Some frames-known as I frames, or intra-coded frames-are processed without regard to surrounding frames, and are compressed the least because they serve as a reference point. I frames define the first in a group of pictures (GOP) usually numbering 12-15 consecutive frames. Next in the GOP is the B frame, or bi-directional interpolated frame. B frames refer to neighboring frames in the group preceding and following the B frame, detecting a maximum amount of redundant information to be discarded. In a typical GOP of 13 frames, B frames comprise more than half the total. This reduces the data stream very efficiently. P frames-predicted frames- refer backwards to the preceding I or B frame for a comparison of redundant information, which is discarded. Compression of P frames is not as aggressive as that of B frames. MPEG-1 provides 352 x 240 resolution at 30 frames per second, with quality equivalent to VHS videotape, when proper compression techniques are used. The 352 x 240 resolution is typically scaled and interpolated. (Scaling causes a blocky appearance when one pixel-scaled up-becomes four pixels of the same color value. Interpolation blends adjacent pixels by interposing pixels with "best-guess" color values.) Most graphics chips can scale the picture for full-screen playback, however software-only half-screen playback is a useful trade-off. MPEG-1 enables more than 70 minutes of good-quality video and audio to be stored on a single CD-ROM disc. Prior to the introduction of Pentium® processor-based computers, MPEG-1 required dedicated hardware support. Today, Microsoft Windows 95 supports the MPEG-1 format through the ActiveMovie API, and Pentium processors with MMX™ technology are ideal for smooth software playback of MPEG-1 video. MPEG-2 has a resolution of 704 x 480 at 30 frames/60 fields per second, four times greater than MPEG-1. It is optimized for the higher demands of broadcast and entertainment applications such as DSS satellite broadcasts and DVD players for home theater. At the time of this writing, there are no personal computers available that are powerful enough to play back MPEG-2 without dedicated hardware. Several IBM ThinkPad models include a Media Processor for hardwareassisted MPEG-2 video playback at Half Horizontal Resolution (HHR). HHR provides excellent video playback scaled to full-screen XGA (1024 x 768) resolution without the storage demands of full MPEG-2. In addition, IBM anticipates that the ThinkPad 770 will include a DVD drive capable of playing MPEG-2 encoded movies at full screen resolution. The MPEG-2 standard is backward-compatible with the MPEG-1 standard, thus any system equipped for MPEG-2 playback will also be able to handle MPEG-1 video. DVD means business The DVD specification is as versatile as its storage is vast. The features that are so appealing to consumers for entertainment purposes are equally useful in a myriad of business applications, from archiving huge databases, to multimedia presentations, to interactive training. Even before the advent of DVD, digital video had proven a uniquely effective medium in conveying complex information. Although widely acknowledged as the tool of choice for many applications, the storage demands of digital video limited its use to short clips on CD-ROM, usually at quarter-frame resolution. Those constraints are now behind us. With MPEG-1 and MPEG-2 encoding, digital video on DVD should become as universal as the VHS tape cassette. Beyond its huge storage capacity, DVD has other advantages that will most likely benefit business users even more than consumers of home videos. The following feature/benefit scenarios, although seemingly obvious, are merely speculative. It remains to be seen which features will September 1997 4