Racelogic VBOX LITE Hardware & Software Manual - page 15
VIDEO VBOX LITE MANUAL
Page | 15
22 December 2009
MPEG4 Video
The Video VBOX LITE records interlaced MPEG 4 AVI Files.
NB: It is not possible to record video when the Video VBOX LITE is connected to a computer. If the ‘Rec’ button is
pressed whilst connected to a computer via USB the Video VBOX LITE will produce a warning beep.
Interlaced Video
There are two methods of recording and displaying video footage: interlaced scan and progressive scan. At the
moment, the only bullet cameras you can buy use interlaced video:
•
Interlaced scan:
This technique uses two fields to create a frame. One field contains all the odd lines in the image, the other contains
all the even lines of the image. A PAL based television display, for example, scans 50 fields every second (25 odd and
25 even). The two sets of 25 fields work together to create a full frame every 1/25th of a second, resulting in a display
of 25 frames per second.
•
Progressive Scan:
This technique displays video by drawing all the lines of each frame in sequence. It is used for most cathode ray tube
(CRT) computer monitors, all LCD computer monitors, and most HDTVs as the display resolutions are progressive by
nature. (Other CRT-type displays, such as SDTVs, typically display interlaced video only)
The Video VBOX LITE creates interlaced MPEG4 AVI format video files.
Interlaced video is designed to be captured, stored and displayed in the same interlaced format. Because each frame
of interlaced video is composed of two fields that are captured at different moments in time, interlaced video frames
will exhibit motion artefacts if the recorded objects are moving fast enough to be in different positions when each
individual field is captured. These artefacts may be more visible when interlaced video is displayed at a slower speed
than it was captured or when still frames are presented.
Because modern computer video displays are progressive scan systems, interlaced video will have visible artefacts
when it is displayed on computer systems when there is a fast moving object in the frame. Computer systems are
frequently used to edit video and this disparity between computer video display systems and television signal formats
means that the video content being edited cannot be viewed properly unless separate video display hardware is
utilized.
NB: If the video recorded by the Video VBOX LITE is played out to a television capable of displaying an interlaced
source the interlacing is not visible and the quality is exceptional. Replaying the recorded video on a CRT or LCD
monitor may require software filters to be applied to smooth out the interlacing otherwise objects in the video will
appear ‘combed’ or jagged.
If the video is to be played back on a progressive scan monitor (ie. computer) then mounting the main video camera
pointing directly forwards out of the car reduces the frame to frame differences and the interlacing effects are
reduced if playing back on a computer. The video bitrate is also better utilised recording detail instead of motion blur,
as video bitrate varies tremendously depending on what is being recorded.
Windows Media Player does not render the video as well as other media players, Racelogic recommend the free to
download VLC player (
http://www.videolan.org/vlc/
) as the quality of the rendered video is much higher. VLC player
also has the ability to enable a de-interlacing filter (Video De-Interlace Blend).
For a detailed explanation of interlacing also see here:
www.100fps.com