One way to understand today's connections is to put them into four different groups:
Common AV Connections
Just as it is possible to put today's connections into four groups, it is also possible today's AV connections into four groups: analog and digital audio-only connections, analog video connections on consumer electronics (CE) devices, the analog Video Graphics Array (VGA) connection on personal computers (PCs), and digital video connections. These four groups are discussed in more detail below:
The discussion above is summarized in the table below with some additional info:
|RF||Analog||CE||Audio and video|
|Composite||Analog||CE||Video, improved quality over RF|
|S-Video||Analog||CE||Video, improved quality over RF and composite|
|Component||Analog||CE||Video, highest quality analog connection for CE devices|
|DVI||Digital||PC||Video, requires conversion to HDMI to carry audio|
|Audio and video, although some older receivers did not process the audio portion |
|DisplayPort||Digital||PC||Audio and video, although some early DisplayPort-equipped products didn't output audio over DisplayPort [7 page 18] |
If you want to find out more background information about the various AV connections that are used today, two good pages to check out are Crutchfield’s Home A/V Connections Photo Gallery (the RF connection is shown in the "75-ohm coaxial" pictures) and Monoprice’s Video Compatibility Matrix.
Monoprice’s page does, however, have some problems. First of all, Monoprice says that DVI stands for “Digital Video Interface”  when in fact DVI stands for “Digital Visual Interface” [10 page 1]. Another mistake Monoprice makes is saying that if you convert DVI to HDMI you’ll still need a separate audio connection. As discussed above, this is not always the case. Finally, for the picture of the composite connection, the yellow plug is the actual composite connection - the red and white plugs are the separate analog audio connections often placed near a composite connection.
Coaxial Cable Connectors & Connections
When discussing connections, it is important to distinguish between connections, cables, and connectors. One of the most widely used cables for AV transmission is the copper-based coaxial cable. Because it used so widely, it has different types of end connectors for different purposes. In the world of CE, the three most common end connectors for coaxial cables are the phone connector, the RCA connector, and the F connector     .
The phone connector comes in three different sizes: 2.5mm (about 3/32 inch), 3.5mm (about 1/8 inch), and 6.35mm (1/4 inch). The phone connector can also carry one, two, or three signals of information . Phone plugs are often color-coded to help identify usage . Some usages of the phone connector are discussed below (more uses are discussed here ):
The RCA connector comes in one size only and can only transmit one signal. Like the phone connector, color-coding is sometimes used for the RCA connector . The RCA connector can be used to transmit:
Like the RCA connector, the F connector comes in one size only and can only transmit one signal. There are, however, two types of F connectors: screw-on and push-on. Push-on F connectors can be a bit easier to connect but screw-on F connectors generally provide better transmission. Color-coding is not used for F connectors. Coaxial cables with F connectors are mostly used to transmit:
Component & DVI Resolution Limitations
Although component and DVI can transmit a 1920x1080p signal, these connections are sometimes prevented from doing so.
First, let's look at component. As described in the Aspect Ratio article, having an upscaling DVD player is handy because it vastly simplifies the process of dealing with DVD aspect ratio. Unfortunately, DVD and BD players today are limited to 480p/576p over component for copy-protected DVD video output , thus not allowing easy aspect ratio handling with a component connection. DVDs without copy protection can be output at up to 1920x1080i [16 pages 13 and 83]. As for BDs, while initial BD players were allowed to output BDs at up to 1920x1080i, players made in 2011 or later are only allowed to output BDs at 480i/576i , which is even lower than what is allowed for DVDs. Finally, even if you have a BD player made before 2011, component output can still be lowered to 960x540p if a BD uses what is known as the Image Constraint Token . This information is summarized in the table below:
|1080i for non-copy-protected DVDs||1080i for pre-2011 players||960x540p|
|480p/576p for copy-protected DVDs||480i/576i for 2011 and later players|
Next, let's look at DVI. As discussed in the Optical Disc Playback and Copying Problems article, High-bandwidth Digital Content Protection (HDCP) is copy protection designed to prevent both unauthorized recording AND unauthorized viewing of video over a digital video connection. The major problem for DVI is that DVI was created before HDCP, so some DVI connections are not HDCP-certified. More specifically, DVI was finalized on Apr. 2, 1999 [10 page 1], but HDCP was not finalized until Feb. 16, 2000 . Furthermore, the first HDCP-equipped products did not come out until June 13, 2000  and did not REALLY start to come out until 2001 . Unfortunately, even some DVI-equipped products produced well after 2001 do not have HDCP compatibility . This level of uncertainty is not present with HDMI and DisplayPort connections since just about every HDMI and DisplayPort-equipped device also supports HDCP.
If a device with a DVI connection that is not HDCP-certified is connected to an HDCP-certified display, you may have to lower the resolution over DVI down to 480p/576p when watching copy-protected content , or you may not even get a picture at all . Should the first condition occur you may be better off with an analog connection, and if the second condition occurs you are definitely better off with an analog connection. One only needs to look at the table above to see why this is the case: a pre-2011 BD player would be able to output 1080i over component for BDs, but due to HDCP would presumably be limited to 480p/576p BD output for non-HDCP certified DVI.
Another way to demonstrate that component may give you a higher resolution than non-HDCP DVI is to look at the component and non-HDCP DVI scenarios for the Xbox 360. This is shown below:
|DVD ||HD DVD ||Games ||Netflix |
Length & Image Degradation
When it comes to cable length, the one simple rule is this: the longer the cable, the more likely you are to see image degradation. That being said, analog connections and digital connections degrade in different ways. While an analog connection degrades in a manner that is “progressive and continuous,” a digital connection “can exhibit no functional degradation at all up to a point.” However, once that point is past, “the digital signal begins to fall apart, and not long after that… there is no signal at all” .
When an analog signal travels from a source device, such as a DVD player, to a destination device, such as an HDTV, not only is the signal subject to degradation from having a longer cable but also from interference from surrounding devices. This interference may show up as audio buzzing or rolling bars across the picture.
A digital AV connection is much less susceptible to interference than an analog AV connection. That being said, any AV connection using a copper-based cable still has the possibility of picking up interference, analog or digital. The only way for an AV connection to completely avoid interference is to use an optical cable, which uses light instead of electricity to transmit information. Optical cables, however, are susceptible to problems caused by bent cables, something that doesn't really affect copper-based cables .
Source Device vs. Receiver Digital-to-Analog Audio Conversion
Although analog AV connections are more subject to degradation than digital AV connections, one reason it may still be better to use an analog audio connection would be if your source device does a better job of digital-to-analog audio conversion than your receiver. Digital-to-analog audio conversion is needed for digital audio since today’s audio speakers are inherently analog devices  .
The part of a device that converts digital AV information to analog is known as a digital-to-analog converter (DAC).
If you are using a digital audio output from your source device to your receiver, then you are using your receiver’s DAC.
If you are using the analog audio output on your source device, then there are two possibilities. On the one hand, it is possible that you are only using your source device’s DAC for audio. On the other hand, it is possible that you are using your source device's DAC for audio but that the receiver then converts the audio BACK to digital using an analog-to-digital converter (ADC) and then again to analog using its own DAC. In order to avoid this extra ADC-DAC conversion, some sort of special mode may have to be selected on the receiver such as Harman Kardon’s “Analog Bypass Mode” [31 page 35] or Pioneer’s “Analog Direct” [32 page 138].
So, does using your source device’s DAC instead of your receiver’s DAC justify using an analog audio connection? Probably not.
The major problem is that multichannel analog audio outputs are not available on many devices and multichannel analog audio inputs are no longer available on many receivers , restricting analog audio usage to stereo only. Even if there is a multichannel analog audio input on a receiver, there is usually only one.
There are two other points to consider as well. The first is that even if one DAC is technically better than another DAC, you might not hear a difference. The second is that, at a certain point, audio becomes “good enough” and you may no longer hear any quality differences regardless of the DAC used. Taken together, these two points mean that even if your player’s DAC is technically better than your receiver’s DAC, in reality you might not hear a difference.
To illustrate these two points, let’s look at Oppo’s BDP-93 and BDP-95 BD players. When comparing the audio distortion of the BDP-93 and BDP-95 DACs, Gene DellaSala of Audioholics writes that “yes there were slight measurable differences between the players with respect to distortion, but it’s very unlikely there would be a situation where these differences would be audible” . In regards to crosstalk, another audio characteristic, DellaSala writes that comparing “the audible differences with regards to crosstalk between these two players would be like trying to compare the loudness of a gnat’s fart in loud New York City traffic if one listener was sitting in Florida and the other in Australia” .
Digital Display Digital Video Defects
Unlike audio speakers, today’s non-CRT displays are digital devices and therefore should always work better with digital video connections compared to analog video connections. Sometimes, however, digital displays will give a better picture with an analog video connection. Inferior image quality from the digital video input can occur if, for the digital video input, a display enlarges the video images beyond the borders of the display (known as overscanning) and/or uses incorrect video processing. Sometimes this is correctable , while other times it is not.
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