Tuesday, January 05, 2010

Various video interfaces and their qualities

There are so many types of video interfaces (ie., cables) that we come across every other day and not everyone understands what they are. It is essential to understand them, so we can use the best option that we have. There is definitely differences in the video quality and because these standards have evolved over time, not all video devices (be it a TV or a video player) have all available options. This has enforced the recent device manufacturers to support a variety of video interfaces, thus they ensure backward compatibility with the other end (a TV or a player). Unfortunately this has brought in confusion to the common people when they just look at the back of their new LCD TVs. Those olden days TV would just have one RF cable input, nothing else!! Gone are those days! Now, if you look at a modern TV, there are whole bunch of outputs (yes, including that RF cable input), and it isn't easy to choose the right cable to use for your need unless you understand what it means. Thanks to all those unique swanky colors, that lets us easily identify them on two devices.

It so happens that if both your devices (player/TV) are recent ones, you will have many choices. At that point, it becomes important to use the right one. Here are the various cables in the increasing order of their quality:

1. RF coaxial cable: This is the old one, that used to run from the Antenna on the terrace. This has the least quality. The TV Tuners for computer are exactly meant to decode this input. Carries both audio and video.

2. Composite (RCA): This is the most popular yellow plug thingy. Composite cable offers more quality than the coaxial ones. This is so very popular that, people still use this for video signals even when they have better options. That said, even today, this is still the most available option (in India). Many lower end DVD players/TVs only support till Composite. Carries only Video.

3. S-Video: The name apparently derives from the phrase 'Separated-Video'. In S-Video, the video signal is mainly separated into two parts: Chrominance (color) and Luminance (light intensity) signals. This offers much better clarity while solving some shortcomes in the composite signal. S-Video cable appears as a single cable, but has multiple terminals within it. Quality better than Composite. Not so commonly seen/used on TVs/players. Carries only Video.

4. Component: As it's name indicates, component video carries various components of the video separately. It is an enhancement over S-Video, by splitting the video signal into Chrominance (color) and 2 Luminance (light intensity) signals. And the luminance signal carries the subtraction of luminance and the Chrominance (Y). The signal is carried via 3 cables (Green, Blue and Red). The component video input/output is usually marked with Y, PB/CB, PR/CR. The second and third channels are actually B-Y, and R-Y respectively. This subtraction method reduces the bandwidth requirement and offers much more clarity than any earlier ones. This is becoming increasingly available these days (my Tata Sky Plus STB has component out). The clarity is apparent (against Composite/S-Video) when the size of the display is bigger and when the source of the signal is digital (note: Component signal is not digital, it is analog; I'm talking about the source of the signal, say MPEG2/4 as in DTHs). There is also a RGB Component video, which carries the R, G and B signals separately in 3 cables; but unless qualified with RGB, a Component video means the normal one. Quality better than all the above. Carries only Video.

5. DVI: Acronym for Digital Visual Interface / Digital Video Interconnect. Provides really high bandwidth to transfer high quality video including full-HD (1080p @ 1920x1080). DVI uses a single high quality cable with a number of internal lines. DVI has a quality much superior than that of component video too. DVI does not carry audio signal -- usually a preferred interface for computer to high resolution LCD monitors.

6. HDMI: Acronym for High Definition Multimedia Interface. There are various revisions on this video standard and this is the state-of-the-art video interface standard as of today. Unlike DVI, HDMI carries both video and audio. The video quality is just the same as DVI, and it also has provision to carry signals for 8 audio channels!! In addition it also carries a commanding control line (called CEC - Consumer Electronics Control) which allows the HDMI devices to communicate and command each other. To quote an example, when I turn off my LCD TV, it automatically turns off my Home Theatre (yes, both are connected by HDMI). HDMI-CEC is usually called in different names by different TV/Home theatre manufacturers. For eg., LG calls this SIMPLINK. This is a really high-bandwidth interface and requires a good quality cable for best results -- the cable is pretty costly; as of this writing a good HDMI cable of 3m length costed me Rs.800 in Bangalore. An interesting note is that: DVI and HDMI are compatible with each other at signal levels too, so it is pretty easy to get converters between them -- obviously HDMI-to-DVI will result in loss of information on audio, CEC on the receiving end.

The bottom line is: If you ever have a means to connect via HDMI, just do it! else, follow this ordering by quality and choose the right one. In my home, I have my home theatre connected to my TV via HDMI (I can watch full HD movies with Dolby Digital audio, with just that one cable running between them) and my Tata Sky Plus STB connected to my TV via Component.


  1. Gerald,
    This is an awesome post. The reason I say that is because I am always at sea when people talk about video cables! You made is so simple for me to understand and I came to know of all options available in one post.

    Let me see if I got this right. At my home the cable from the cable operator that connects to my TV is a RF coax. While I connect my music system and dvd player to my Videocon TV using component cables.

  2. Vittal,

    Glad this was useful for you.

    I can't totally confirm whether your identification of cables is correct unless I see them; but yes, you are most likely correct.