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Thursday, April 22, 2004
Aopen XRecorder

3. Inputs / Outputs

AOpen XRecorder VX2000 - Page 3

XRecorder Connections

The unit features a complete set of inputs for connecting a number of devices to capture video from: S-Video or Composite Video In, stereo audio input, cable TV/aerial antenna TV input. Last but not least, an IEEE1394 input is there if you want to connect a DV camcorder. All the connectors except the TV input are located in the front making connecting/disconnecting cables easier. All the necessary cables were included in the packaging, so you don’t need to buy any extra cables to connect your video sources.

The front panel of the XRecorder is shown in the following picture.

As can be seen in this photo, there are three choices of input available for video capture. From left to right we have:

  • the infra-red remote control detector
  • then in turn the IEEE 1394 DV input
  • next are the left and right sound channels (white and red RCA plugs)
  • composite video input (yellow RCA plug)
  • finally, the S-video input (4-pin DIN plug).

You would connect your external video source device such as a DVD player, VCR, camera, etc using one of these connections.

The following picture shows the rear panel.

Here we have the power input (5V DC), 75 ohm IEC coaxial input (cable TV antenna), USB port which connects to your PC, and on the far right the on/off switch.

The following diagram shows the possible source devices and how they can be connected to the XRecorder, and the USB connection which is here shown going to a portable PC.

How a video signal is generated

The three primary colours used in broadcast TV systems are red, green and blue or RGB for short. The proportions in which they are mixed however is not equal. The equation 0.30 R' + 0.59 G' + 0.11 B', corresponds to the human eye's sensitivity to each of the three colours. When combined in these proportions, they produce one signal, called the luminance signal. In fact, that is how a black and white TV works. All it shows is the contrast in a picture, without the colour information. When colour TV came on the scene, one of the criteria was that a colour signal had to still be compatible with black and white TVs which were still in use. All a black and white TV does, is to take the luminance information in the transmitted signal and discard the colour portion.

Next, in order to create the colour or chrominance signal, the three separate RGB signals are again combined in the following proportions to produce two new intermediate signals.

I = 0.74 (R'-Y) - 0.27 (B'-Y) = 0.60 R' - 0.28 G' - 0.32 B'
Q = 0.48 (R'-Y) + 0.41 (B'-Y) = 0.21 R' - 0.52 G' + 0.31 B'

The I and Q signals are bandwidth limited and separately modulated onto a carrier with frequency of 3.58 MHz and 90 degrees out of phase with each other. The resultant signals are then added together producing a quadrature amplitude modulated (QAM) chrominance signal.

S-Video input

S-Video specifications

As was stated earlier, S-Video provides much better quality as compared to a composite connection because the brightness signal (Y) which carries clock pulses travels separately from the color signal (U, V), thus preventing color crosstalk aberrations, along with a frequency bandwidth of 6 MHz ensuring higher sharpness at 500 lines.

Composite video input

Used for composite signal transmission, today, most TV sets have at least one composite video input, characterised by the yellow RCA plug. It is used for transmission of video along with audio (on separate connectors coloured white and red). The bandwidth supported is narrower than that of S-Video being only 4.2 MHz, hence the low sharpness. The bearer is a single wire with shielded earth, requiring that the colour and brightness or luminance signals be mixed. Because the two signals are mixed, they require separation at the receiver. The separation is never perfect due to the overlap of some frequencies from both signals when they are originally mixed producing a form of color crosstalk aberration, something that is noticeable in contrast details.

DV input

Digital Video, also known as DV, IEEE 1394, FireWire and i-link. Video that has been produced by a DV camera for example, and can be easily imported into a computer for editing or encoding. The video is sampled at the same rate as D-1, D-5, or Digital Betacam video, although the color information is only half the D-1 rate: 4:1:1 in 525-line (NTSC), and 4:2:0 in 625-line (PAL) formats. DV images are compressed but use a superior technique to motion-JPEG, allowing for higher-quality 5:1 compression. DV video data is transmitted at a guaranteed rate (known as isochronous), which is a feature of the IEEE 1394 bus, supporting data transfer rates of up to 400Mbps (1394a) and 800Mbps (1394b).

Connect your camcorder to the XRecorder and then save your videos to your PC through the XRecorder. Because the XRecorder performs the compression for you (and at a very high quality), you save on both disk space and processing time/power.

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