ZeeVee ZvBox 170 Front Panel - Manual (Page 11)

ZvBox ® 170 Configuration Manual Page 11
www.zeevee.com Rev 1.0
Select Underscan Resolutions to Present in VGA EDID
When ZvBox® 170 is connected to a computer via the VGA connector, ZvBox® presents to the
computer’s graphics card a set of resolutions that are supported by ZvBox®, including the 1280 x 720
resolution used by HDTVs. These resolutions are presented in a structure called EDID (Extended Display
Identification Data). If ZvBox® is broadcasting a full 1280 x 720 resolution to an HDTV that “overscans”
(crops off the edges of the picture), important information may be lost, e.g. a PC taskbar or a scrolling
ticker at the bottom of the screen. In that case it’s possible to choose a ZvBox®‐supported “underscan”
resolution at the PC, generating a slightly smaller picture that will remain within the viewable area of the
HDTV screen.
The following command allows you to set an underscan resolution for 720, which will be communicated
to your PC via EDID. Once an underscan resolution has been selected, you may set your PC’s output
resolution to that resolution.
Note: each TV will perform a different amount of overscan, so keep this in mind when selecting an
underscan resolution. It can be useful to have the ZvBox® output test‐image‐1 (i.e. “set video‐source
test‐image 1”) when determining the correct underscan resolution.
Syntax
SET VGA‐RES {1264x711 | 1248x702 | 1232x693 | 1216x684 | 1200x675 |
1184x666 | 1168x657 | 1152x648 | 1136x639 | 1120x630}
MPEG2 Encoding Control
This group of commands can be used to fine‐tune the characteristics of the MPEG2 encoder. The factory
defaults have been set to values that produce the best picture, while also maximizing the chance that all
HDTVs will correctly display the encoded video. We have found that some HDTVs are sensitive to certain
things like total bit‐rate or number of bits of DC coefficients. The picture may sometimes break up, or in
some cases not display at all!
Experimenting with these settings can improve the quality of the encoded video, but we strongly advise
you to test any changes on *each type of HDTV* that may receive the signal.
Set Encoding Bit Rate
A digital cable (QAM) RF channel allows for a data rate up to 38.78 Mbps. Usually, that stream is divided
into multiple digital channels, each having a lower effective data rate. Since ZvBox® is placing a single
digital channel in the stream, it can send more data during complex scenes, up to the 38.78 Mbps limit.
This can result in significant improvements in video quality for certain very complex scenes. However,
some HDTVs will experience some picture breakup if the data rate ever exceeds 19.4 Mbps for a single
digital channel. We have observed that this is true of some Sharp HDTVs, and may be true of others.
“Normal” will keep the encoder’s output data rate to 19.4 Mbps. High will allow the encoder to operate
up to 38.78 Mbps. At this time, Low and Normal have the same effect.
Syntax
SET DATA‐RATE {low |normal | high} factory default: high