 syntax had emerged. It defines a standard input Video Communications: The Whole Picture format (SIF) that can be used to produce audio and video samples that are coded and compressed at a bit rate that is not to exceed 1.86 Mbps. Image sizes can be no larger than 720 pixels by 576 lines (although it is syntactically possible to encode picture dimensions as high as 4095 lines by 4095 pixels). In fact, MPEG-1 images are usually 352 pixels by 240 lines. They are captured using progressive scanning (such as is used by computer monitors). MPEG-1 samples two channels of audio, combines it with the video and delivers it (either over a direct connection to a CD-ROM storage device or via a telecommunications network connection). After demonstrations proved that the syntax was flexible enough to be applied to bit rates and sampling frequencies much higher than those required for CD-ROM playback applications, a second phase (MPEG-2) was initiated within the committee. Its objective, to define a syntax for the efficient encoding of interlaced (broadcast) video, was more difficult to achieve than that of encoding progressive scanned images. Audio encoding also presented a challenge. MPEG-2 would introduce a scheme to decorrelate multichannel discrete surround sound audio. In 1991, it appeared that HDTV had special needs that would require a separate syntax. Thus, plans were laid to define MPEG-3. Tests in late 1992 revealed that the MPEG-2 syntax would, with a small amount of fine-tuning, scale with the bit rate, obviating this third MPEG phase. As a result, MPEG-3 was merged into MPEG-2 in 1992. However, most music sites on the Internet now use MPEG-3 because its file sizes are approximately 30% smaller than are those of MPEG-2. MPEG-4 (ISO/IEC 14496) was launched in late 1992 to explore the requirements of a more diverse set of applications. Its goal was to find a syntax that could be used to code very low bit rate (4.8-64 Kbps) audio and video streams. MPEG-4 encoding is aimed at videophone and small-screen terminal (176 