Hardware Reference
In-Depth Information
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Digital Media Controller. A DMC enumerates the content on a DMS, and sends a “play”
request to a media renderer.
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Digital Media Renderer. A DMR accepts content that is pushed to it, by a DMS, as instructed by
a controller (DMC).
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Digital Media Printer. A DMPr is the DLNA equivalent of a self-glorified networked printer.
It could be considered as a “write-only” DMR, working until the control of a DMC or DMP.
As with UPnP, some devices combine two or mor, pieces of functionality in the same physical box.
Most software-based UPnP devices are also DLNA compliant but haven't paid the licensing fees to be formally
licensed as such.
AirPlay
Originally called AirTunes, back in 2004, this Apple-originated equivalent of UPnP and DLNA allows for media
streaming between all compatible devices. However, being Apple, such streaming is only possible if you own an Apple
device and software or one of the few third-party licensed products entering the market. Consequently, it has had little
take-up in the Open Source world, and even projects such as ShairPort, which attempt to emulate an Airport express,
have faltered.
The only benefit of AirPlay in an Linux-based house is to provide a closed network for the kids to access media.
You can have an open UPnP environment for the master bedroom and living room (where viewing habits can be
socially policed), and an AirPlay one for the kids.
Distribution
This is the third step of our data chain. Once we have our media data served and decoded, we are left with an AV
signal ready to be plugged into a TV or HiFi. But we still have choices.
Local Processing versus Remote Processing
The equipment covered earlier is all locally processed. That is, we decode the data in a location that is physically
connected to the TV or HiFi. This is usual, as it gives us greater fidelity and means that controlling the unit is much
easier, but there are cases in which the processing is better done remotely and only the resultant AV signal is sent.
AV Distribution
The output from nearly all media playback devices is our first port of call. This usually comprises RCA phono sockets
for stereo audio or composite video, S-Video, EIA interface, SCART, or something of that ilk. This carries a fairly low-power,
analog signal over short distances to an amplifier—be it TV or HiFi. Because these signals always need a power
amplifier, we call this
active distribution
.
Providing distribution in this manner requires various interconnects and many cables. There is no upper limit
on the length of these cables, so extensions and distribution boxes are possible, allowing the same image to be viewed
in multiple places. Naturally, being an analog signal, the audio (or picture) will become softer as you get farther away
from the source. Only you can determine what quality loss is acceptable for you.
If you are wanting to distribute high-definition images around your house, then you currently have to consider
the more expensive options, such as matrix switchers, because the current crop is focused around RCA sockets.
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