The Amnis NAC 3000 encoder and NAC 4000 decoder were the best performers in our tests. The NAC 4000 handled just about every problem we threw at it. In addition, the NAC combo has one feature for providing the best quality video that the other products don't have: The NAC 3000 and 4000 can perform limited packet retransmission, providing better picture quality in limited-loss situations (but not in our tests). In our reorder test, the NAC 4000 properly presented the video without any dropped frames or missed pixel groups. This was true even though up to 40 percent of the packets were being reordered. These results were duplicated only by a Minerva VNP loaded with beta firmware.

What also sets the NAC 4000 above the rest is its ability to handle a network's latency deviation. Amnis built its decoder with a buffer large enough to handle a 480-millisecond deviation in latency. We added 20 ms to 500 ms to every packet, and the NAC 4000 presented a crystal-clear picture. With this equipment, even the worst networks can get good-quality video from source to destination.

This beautiful video doesn't come by default, however; the audio and video buffer sizes have to be increased. Amnis also offers a method of retransmitting lost packets when configured on both the encoder and the decoder. This is useful only in unicast sessions, as requests for lost multicast packets could easily overload a network.

Although the NAC series is the best of the lot, we had some problems with the interface. To change the buffer sizes, for example, we had to TFTP a modified config file to the unit. The rest of the interface also needs some work. Amnis provides software called LiveMap to check the units' status and make changes via SNMP MIBs, but we found it easier to navigate the telnet interface. We hope Amnis hides the SNMP underpinnings in future releases of the software. We were also annoyed that, though the decoder will output an S-Video signal, the encoder will accept only a composite signal as input.

To balance the bad with the good, the NAC 3000 let us make changes to the video bit rate on the fly -- no need to stop and restart the encoder. Only the GDC MAC 500 allowed the same on-the-spot handling. Both the encoder and the decoder accept balanced and unbalanced audio and will sample at a variety of rates, so we could fine-tune the amount of bandwidth we used.

The NAC 3000 handles MPEG-1 and MPEG-2 encoding and compression, realizing 24 different resolutions available for transmission. Video bit rates can be set as low as 2 Mbps or, for true broadcast-quality video, as high as 15 Mbps.

For streaming content to the desktop, Amnis' LivePlayer software lets an MPEG-1 stream be displayed on a Microsoft Windows-based computer. For MPEG-2 streams, Amnis, like Optibase, requires an optional decoder card in each computer that's displaying the output.

The NAC 3000 and 4000 are small units -- just 1U each. They can be placed side by side. Depending on the need, Amnis provides different versions of the encoder: one for MPEG-1 only, and the one we tested, with MPEG-2 and large buffers for high-latency situations.

NAC 3000 Live Streaming Video Encoder, $6,995 to $16,995 (based on configuration); NAC 4000 Live Streaming Video Decoder/Receiver, $2,995. Amnis Systems (formerly Optivision), (650) 855-0200, (800) 239-0600; fax (650) 855-0222. www.amnisinc.com