MagicITX :: Content :: Tutorials :: Installing MythTV

Hardware

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In this section we describe the hardware used for the project.

Our MythTV system uses the following hardware:

Case Casetronic C-137

Motherboard: VIA EPIA M10000

CPU: C3 w/ Nehemiah core

RAM: 256 mb

Hard Drive: Seagate Barracuda 120 gb

Optical Drive: Panasonic CD-Rom/DVD Slot-load drive

Video Capture: Hauppauge WinTV PVR-250

Before we discuss the individual hardware components, let's go over the specific tasks the system must perform. The video signal in your coax cable is an analog signal (in the US anyway). Even if you have digital satellite or cable TV, we will be dealing with the signal coming out of the cable or satellite converter box which is analog. So the first thing the system must do is convert this analog signal into a digital data stream. That is the job of the video capture card.

So the video capture card takes the signal from your coax cable and converts it to a digital data stream. This raw digital data stream is huge. Assuming a resolution of 720 x 480 pixels (NTSC), 2 bytes per pixel and 30 frames per second, we have a data stream of 720 x 480 x 2 x 30 = 20,736,000 bytes per second. That's over 74 gigabytes per hour. While high performance desktop systems may keep up with that amount of data it would quickly fill even the largest hard drives.

To make the video data easier to process and store, most systems compress the data to reduce the amount of data moving through the system. The most common video compression scheme is MPEG-2.

There are two ways a system can compress the video signal - via software or hardware. Both methods have advantages and disadvantages which we won't explore here. Suffice it to say that software compression places a heavier load on the system's CPU. Since we want to use a relatively low power system, software compression is not our first choice. In our case the video capture card also incorporates hardware to perform MPEG-2 compression on the video signal.

Once the video signal is digitized and compressed, the system stores the data on the hard drive. As far as MythTV goes even "live" video is first stored on the hard drive. If we're recording a show that's the end of the major processing.

When we want to watch the video, either as a recorded show or as live TV, we basically reverse the process used to store the video. The video data is first read from the hard drive. Next the data needs to be decompressed to restore the raw digital data. Finally the system converts the raw digital data to an analog video signal. This signal is output to your TV.

The same compression options we had on the input side apply on the output side. We can either decompress the signal with software or hardware. The VIA EPIA mainboard includes hardware MPEG-2 decoding. We will want to make use of this.

Finally the decompress digital video stream must be converted to an analog signal for viewing. The system can use its display capability to display the video on your monitor. However since we want to incorporate our MythTV system into our home entertainment system, we want the video output in a form our television understands. Fortunately the VIA EPIA mainboard also includes TV-Out capability.

This diagram shows how the video data stream moves through a MythTV system.

The Motherboard

VIA has a series of motherboards and CPU's positioned for use in embedded and digital media applications. They are noted for their low power requirements, low heat, and low noise. This makes them particularly well suited for our MythTV project.

We are using the VIA EPIA M Mainboard with the C3 Nehemiah processor operating at 1ghz. Unlike some VIA CPU's, the C3 requires a CPU fan.

The CPU might sound a little anemic compared to the multi-gigahertz animals from AMD and Intel. But the cool features of the VIA motherboard goes beyond the CPU. Also included on this motherboard is the CLE266 "North Bridge" chip. The North Bridge chip is the interface between the CPU, memory, video output, and the South Bridge chip. The CLE266 goes beyond this to include 2D and 3D graphics engines plus MPEG-2 decoding. This latter feature is particularly interesting for our system.

The South Bridge chip handles most of the external interfaces to the computer. On our board this is a VIA VT8235 chip. In addition to the USB ports, Ethernet controller, PCI controller, the VT8235 supports 6-channel audio.

Finally, the VIA EPIA M Mainboard includes a TV-Out connector so we can connect our system directly to a television.

Memory

I was ready to go with 512mb of RAM. When you're processing and moving a lot of data I figured that the more memory the better. However during my research for this project I read that MythTV doesn't really need more than 256mb. Unfortunately I can't find the reference so we'll just have to trust my (usually reliable) memory. Since a lot of the "heavy lifting" of MythTV in this systems, MPEG-2 encoding and decoding the video data, is happening in hardware, perhaps we don't need more than 256mb of RAM. Anyway, that's how I decided on this amount of RAM.

Hard Drive

I guess I'm a Seagate guy. Seagate was the first (to my knowledge) to focus on reducing noise in hard drives. They first delivered Fluid Damping Bearings in their drives for quiet operation. Seagate also has some of the longest warranties for consumer hard drives.

Concerning capacity, size matters. The larger the better. An hour of recorded video takes over 2gb. Of course cost also matters so I went with a 120gb drive instead of the newer 200gb drives.

Note that with a 3.5" hard drive only one of the Casetronic C-137's PCI slots is available. If you want to use two PCI cards, you'll need to use the smaller 2.5" laptop hard drive. These drives do not have the capacity of the 3.5" drives, are slower, and cost more. Later I'd like to see if I can use two video capture cards. This would let me record one show while watching another or record two shows at the same time. I'll likely move to a 2.5" drive in the future.

Optical Drive

Technically you don't need an optical drive after the operating system is installed. There is nothing that MythTV does that needs an optical drive. However we may later want to play DVD's so we'll go ahead and install the DVD drive. If you want to save some money you could skip it for now. You'll need a CD-ROM drive to follow along with our Gentoo Linux installation but you could use about any old IDE CD-ROM drive for that.

The Casetronics case we are using needs a slim optical drive. These drives are 12.7 mm high and typically found in laptops. We decided to use the Panasonic CW-8123-B Slimline Slot Loading CD-RW/DVD-ROM drive. Feature-wise this drive is pretty standard. It has 24x CD reading and writing speed and 8x DVD reading speed. The slot loading is not something you often see on PC's (Mac's have used them for years). There is something appealing to me to have all the important stuff of a drive on the inside instead of having it slide outside. The slot load drive is a bit more expensive than tray loading models..

Video Capture

As we discussed above, the video capture card converts our analog video signal into digital data. The card we're using, the Hauppauge WinTV PVR-250, also processes the video data using hardware MPEG-2 compression.

The technical specifications for are PVR-250 are:

TECHNICAL INFORMATION

Device Type: TV/Video Input Adapter
Supported Resolution: 720x480 NTSC D 1352x240 NTSC MPEG-1720x576 PAL D 1352x288 PAL MPEG-1704x576 1600x1200
Connectors: 1x S-Video Video-in, 1x TV Antenna Type F Connector, 1x Composite RCA Video-in, 1x Mini-Phone Stereo Line-in
Data Transfer Rate: 12MBPS
Bus System: PCI
Supported Video Formats: NTSC * PAL
Frame Rate: 25 Frames Per Second PAL * 29.97 Frames Per Second NTSC
Video Features: - Analog Video Signal: S-Video HF TV Signal
Digital Video Format: MPEG-1 MPEG-2 AVI
Compression Ratio: 100:1
Still Image Format: JPEG BMP TIFF GIF

MPEG RECORD SPECIFICATIONS

MPEG1 Data Rates: 1150K Bits/Sec (VIDEO CD DATA RATE)
MPEG2 Data Rates: 2m bit/sec, 4m bit/sec, 6m bit/sec, 8m bit/sec, 12m bit/sec * Selections for DVD Standards Play (8m bit/sec), DVD Long Play (4m bit/sec), and DVD Extra Long Play (2m bit/sec)
Audio Capture Formats: 32/44.1/48 khz 16 Bit Stereo 192/224/384k bit/sec
Chroma Sampling: YUV 4:2:0
Video File Format: .MPG
Supported Broadcast Formats: NTSC PAL

Assembly

We'll leave assembly as an exercise for the reader. If you need help there you can jump on the forums and ask for help. Below are a couple pictures of our assembled system.

If you need hardware for your MythTV system, you can get everything you need here. We even have a MythTV kit that includes all of the hardware mentioned in this section. By using the same hardware we use we can guarantee you will achieve success.

Next: Part 3 – Base OS

History

9 Feb 2005 Initial Publication

16 May 2005 Added table of contents, link to next section, html cleanup.

Tim

Published on: 2005-01-23 (11122 reads)

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