In
the DVR card market, there are 2 kinds of the hardware
compression cards.
-
One is Single-Video Streaming
card.
-
The other is Dual-Video
Streaming card.
The
Single-Video Streaming card is cheaper than the Dual-Video Streaming
card, but Dual-Video Streaming card can make the remote video
monitoring to be possible.
The reason
why we use the hardware compression card in PC-Base DVR machine is
that we want to get the higher recording speed or the bigger image
resolution. But the video film will become big. Due to the network
bandwidth issue, when we try to send the image to the remote site
from the DVR machine, we need to consider whether we have enough
bandwidth to transfer the huge data of the video streaming by
through the network. The difference of these 2 cards to perform the
remote video monitoring is described below.
1. Single-Video Streaming card
The incoming
video is captured and processed the video compression at this H/W
DVR card. Then, this compressed video data flows to the PC and
stores it into HDD. If the remote site wants to view the image of
this DVR machine, the PC will send out the same data to the remote
site. Due the data stream is very big, we need arrange enough
bandwidth for it. Otherwise, the video stream will be blocked on the
network.
For example,
If we set the recording speed of each camera is 25/30 fps (PAL/NTSC)
at one DVR machine, the video streaming rate of each one camera will
be around 500K bps (bit per second) only under CIF (352x288/320x240)
resolution. Regularly, we need prepare 2 ~ 4 times bandwidth for
this video stream (Cisco recommends us to prepare 4 times of the communication
bandwidth for the data rate). Let us say 2 times. So, at lease, we
need prepare 1M bps for this video stream (Only for 1 camera). It is
meaning that we want to send more camera¡¦s video out to remote and
we need more bandwidth. Most of the remote monitoring will use
internet or VPN. From the above analysis, it is almost impossible to
view several cameras from the remote DVR at one time by through
internet. If the VPN network is used, it need expense a very high
cost to rent a very huge bandwidth to set up a video security
network.
¡@
2. Dual-Video Streaming card
The
Dual-Video Streaming card can offer 2 independent video streams. One
is for the local recording. The other is for the remote monitoring.
To achieve this feature, this kind of card need use 2 independent
image compression engines.
Due to these
2 engines are independent with each other, we can give them the
different conditions to compression the video. For examples, they
can have different frame rate, different compression rate, different
GOP size, even different image resolution.
A brief
function block is shown in the above figure. The engine 1 is used
for local recording. We can set its recording speed at 25/30 fps. To
fit the communication bandwidth, we can set the engine 2 run at 3
fps and transfer its video stream to remote site. By this way, we
can get a high speed recording speed or high image resolution at the
DVR and execute the remote video monitoring in an adjustable video
speed which will be decided by the available bandwidth.
Dual-Video
Streaming is the best resolution to perform the remote video
security in the internet. The Dual-Video streaming cards offered by
most of our competitors only provide one MPEG4 stream and one JPEG
stream, or one H.264 stream and one JPEG stream. But our Dual-Video
streaming cards can offer 2 MPEG4 streams, or 2 H.264 stream. This
advantage can reduce the data rate not only at the local site but
also at the network