Installation guide

Generation of a transport stream for DVB and realisation of a HF-modulated DVB-signal
14 | P a g e
9.1.2 Digital video:
Digital video is a type of digital recording system that works by using a digital rather than an
analog video signal. More specific, digital video is audio/visual in a binary format. Information is
represented as a sequence of digital data, rather than in a continuous signal as analog
information is. Digital video comprises a series of orthogonal bitmap digital images displayed in
rapid succession at a constant rate. In the context of video these images are called frames. We
measure the rate at which frames are displayed in frames per second. Since every frame is an
orthogonal bitmap digital image it comprises a raster of pixels. If it has a width of W pixels and a
height of H pixels we say that the frame size is WxH. Pixels have only one property, their color.
The color of a pixel is represented by a fixed number of bits. The more bits the more subtle
variations of colors can be reproduced. This is called the color depth of the video.
Because of the relatively high bit rate of uncompressed video, video compression is extensively
used. In the case of compressed video each frame requires a small percentage of the original
bits. Nowadays, there are a lot of different compression methods and algorithms. The most
common video compression formats are:
 .MP4
 .AVI
 .MKV
 .WMV
 .FLV
 .MPEG-2
There are two types of compressions. The constant and the variable. At the constant bitrate the
bits per second are kept in a constant rhythm. Each image in the video is compressed the same
and the details and quality of the image can drop in some cases. This type of compression is
usually used in video where we do not need a lot of details or we are not so interested in the
image. At the variable bitrate, the bits per second rhythm is changing. Each image in the video
is compressed differently. Images that have a lot of details and demand of a better quality have
smaller compression comparing to images with less details. This type of compression creates
bigger file sizes but better compressed image quality.
Also, there are two types of displaying the video. The interlaced and the progressive. At the
interlaced the image is projected in alternative sets of lines. The odd-numbered lines first and
then the even-numbered lines and again the odd-numbered lines and so on. While the
progressive display projects the image line by line.
During the digital era, starting in the early 1970s to early 1980s, there is a constant progress in
the quality of the digital videos. It started from simple digital videos of low quality that were
separated depending on the continent that you wanted to use it and nowadays there are videos
of extremely high quality playable everywhere in the world.