VBrick Systems VB6000, VB4000, VB5000 manual MPEG-2 Delay, GOP Length N Reference Frame Distance

Streaming Video Basics

Note Operation with the DSL4000 requires B frames for correct audio/video synchronization.

Table 2. Reference Distance Settings

GOP Length (N)	Reference Frame Distance
	1		2		3
1	†		††		††
2	IP		††		††
3	IPP		IBP		††
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.

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

VBrick Appliance Getting Started Guide 19