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VBrick Appliance Getting Started Guide 19
Table 2. Reference Distance Settings
MPEG-2 Delay
This discussion is relevant only for encoder models ending in –xxx1/–xxx2. Low delay mode
is primarily recommended for conferencing applications. Various video artifacts appear when
content with rapid scene changes is encoded at low data rates in low delay mode. The
reference distance is restricted to 1 (no B frames) in low and medium delay modes. If the
Intrapicture distance is set to 1 (all I frames), video disruptions are minimized, but picture
quality is degraded. With other GOP settings, picture quality is improved, but video
disruption may occur on scene changes. At approximately 6 Megabit video rates and above,
video disruption will not occur, depending on content. In low delay mode, delay will be in the
range of 180–190 milliseconds. Video instability is eliminated at medium and high delay
Note Operation with the DSL4000 requires B frames for correct audio/video
synchronization.
GOP Length (N) Reference Frame Distance
123
1 † †† ††
2 IP †† ††
3IPPIBP††
4 IPPP BIBP IBBP
5 IPPPP IBPBP ††
6 IPP. . . PP BIBPBP BBIBBP
7 IPP. . . PP IBP. . .BP IBBPBBP
8 IPP. . . PP BIBP. . .BP ††
9 IPP. . . PP IBP. . .BP BBI. . .BBP
10 IPP. . . PP BIBP. . .BP IBBP. . .BBP
11 IPP. . . PP IBP. . .BP ††
12 IPP. . . PP BIBP. . .BP BBI. . .BBP
13 IPP. . . PP IBP. . .BP IBBP. . .BBP
14 IPP. . . PP BIBP. . .BP ††
15 IPP. . . PP IBP. . .BP BBI. . .BBP
16 IPP. . . PP BIBP. . .BP IBBP. . .BBP
17 IPP. . . PP IBP. . .BP ††
18 IPP. . . PP BIBP. . .BP BBI. . .BBP
19 IPP. . . PP IBP. . .BP IBBP. . .BBP
†
All I frames.
†† Undefined.