Selecting HardwareBeta

From MythTV Book

Introduction

In this chapter, we cover how to select hardware which works well with Linux and MythTV. Its not possible to document all hardware that works with MythTV, and that's not the intent of this chapter. We will instead provide a general overview, and then provide some recommendations which are accurate at the time of writing this chapter. We also describe our own personal MythTV systems, which gives you an idea of what we have found that works well for us.

One of the more important decisions to make when implementing your MythTV system is what hardware to use. The hardware is certainly the most expensive decision you’ll have to make and the hardest to change if you decide you made an error. The following sections therefore discuss the various pieces of hardware you’ll need to arrange in order to implement MythTV as well as the factors to consider when purchasing. We’ll also discuss the hardware we used when developing our own MythTV systems, which is the hardware we use for all the examples in this book. We’ll also give special attention to areas where you can easily expand your system later. This is so you can start small and grow later -- a well-advised strategy. It also means you can take advantage of increasingly affordable hardware.

Starting Small

Starting small is a great idea because it lets you test the software first and then dedicate hardware (and the associated money that hardware costs) to a MythTV setup. Stewart started really small—he bought the cheapest TV capture card he could find and added it to his existing desktop PC -- an ever-so-loud Pentium 4 that you would never want in the living room. Because Stewart already used Linux as a desktop operating system, it wasn’t a problem to just install MythTV and run the frontend portion only when needed. (The part of MythTV that does the recording -- the backend -- runs in the background, allowing you to run other applications while shows are being recorded.)

Michael’s experience was a little different. After using a TiVo in Australia, he knew he couldn’t live without some sort of PVR technology in his house. Michael bought a new machine specifically for use as a MythTV machine, although he also used it for other tasks such as serving email and sharing files. That original machine was a Dell Pentium 4. After a year or so Michael replaced this will a newer Zalman based AMD system, because it was faster and gave him more expansion options.

However, not everybody runs Linux as a desktop operating system, and not everybody is willing to spend a lot of time trying to get a software package installed and configured correctly. If you want to try MythTV before deciding to build a specific machine for it, then you should look at MythBuntu, which is a Linux LiveCD with MythTV built in. A LiveCD is a CD you can boot your computer from instead of the hard disk, which allows you to run a different operating system than what is installed on the machine’s hard disk without affecting anything installed on your machine. We discuss giving MythBuntu a try more in the next chapter, The Easy Way: Installing MythBuntu.

MythTV’s Architecture

MythTV has two main components: the backend and the frontend. The backend is responsible for capturing video, encoding it, and writing it to disk. The frontend displays a user interface on a TV or computer monitor and allows you to play recordings. The frontend also has several plug-ins available, which perform tasks as various as providing current affairs, web surfing, arcade game console, MP3 playback, and more. Installing Other Plug-Ins covers most of those plug-ins.

Typical MythTV setups include running both the frontend and the backend on the same machine or having the frontend separate from the backend. It’s also possible to have multiple frontends and multiple backends. Running Remote Frontends covers running with more than one frontend.

Selecting a CPU

How fast your CPU needs to be depends on a number of factors. Recording digital TV in its native format (MPEG-2 or H.264) takes up a trivial amount of CPU time, and any CPU you can buy today will happily accommodate several streams. In fact, many analog video capture cards will do the video compression in hardware. Thus, if the machine you are specifying is going to run the backend, you need to be aware of how many video capture sources you intend to have, how many will be recording at any given time, and whether those sources implement video compression themselves.

Encoding analog video as it is recording (especially from lower-quality signals) can take up more CPU power -- even 60 percent of one of the author’s AMD Sempron 2600+ CPUs. Digital capture uses a few percent at most. Standard definition playback can use some CPU, perhaps 10 percent for standard definition, however high definition requires much more processing power. This is mainly because the high definition video frames are each much larger than standard-definition frames. The amount of CPU power required for HD will vary depending on whether the signal is MPEG2 or H.264:

• MPEG2: Typically 60 percent to 70 percent of a Sempron 2600+ will be required . The CPU usage for playback will be lower if you use an X video (xv)–compatible video card, with another decrease for XV Motion Compensation (xvmc) accelerated cards.
• H.264: Requires a very powerful CPU for HD playback. Currently, due to threading limitations within ffmpeg (The library used in linux to play H.264 files), dual core CPUs will generally work better than quad core ones thanks to their higher clock speed. For this reason, if you will be playing HD H.264 video you should select a CPU with the highest clock speed available.

Finally, you need to decide how much post-processing such as commercial detection and transcoding you are going to do on the machine. It is possible to spread this workload across multiple backends, but the most common setup is to have just one backend running with one or more frontends.

A general recommendation is to buy the fastest CPU you can afford, within the constraints of the case and motherboard you have selected. Stewart is currently using an AMD Sempron 2400, and Michael is currently using a AMD Athlon 64 X2 Dual Core Processor 4200+.

If your MythTV box will be sitting in the living room, you don’t want it producing much noise at all. Stewart uses a Shuttle “bare-bones” system (the motherboard is integrated with the case). It’s small, it’s quiet because it has a special CPU heatsink that uses a very quiet fan, and it has all the ports you’d expect on a computer. In regular operation, the loudest part is the hard disk, and you really have to struggle to hear it. Other manufacturers also have quiet cases— some even designed for media applications. Check out the options and remember that if you want more capture cards than you can fit in a small box, you can always add other backends that can be located in rooms where noise isn’t so much of a problem or use USB capture hardware.

Graphics Card

In reality there are really only three manufacturers of chips that drive graphics cards: Intel, ATI, and NVIDIA. Since 3D performance doesn’t matter for displaying TV, you are not going to need a whizz-bang gamer-style video card for your MythTV box. What’s more important is the ability of the card to handle video overlay reliably and do NTSC/PAL video output. Selection can depend on if you are going to be using a DVI/VGA signal to your TV (or computer monitor pretending to be a TV), HDMI, S-Video or composite connection.

Intel is generally rather friendly to the free software community, and its graphics cards are usually well supported. If you can get a motherboard with an onboard Intel VGA or DVI implementation that supports the output you need to get to your TV, these are probably safe bets.

NVIDIA and ATI are another story. They have proprietary, binary-only drivers that they ship for Linux. This does not help the free and open source community at all, and any problems you have while running them will largely be ignored by developers (because they cannot debug the problem with binary-only drivers loaded). There are also free, open source drivers for some ATI and NVIDIA cards -- and since the open source drivers have little trouble with 2D and video overlay, they are quite suitable for MythTV work. We recommend you give the open drivers a try as your first option and fall back to the closed drivers only if you absolutely must.

For NVIDIA cards, there is the free nv driver and the closed source nvidia driver. The free program nvtv can enable TV-out through composite/S-Video for some NVIDIA cards. The proprietary NVIDIA driver will work with more cards and support 3D acceleration as well. The 3D support is not necessary for MythTV; but if you use your frontend machine for other purposes, this might be more important to you. For the typical appliance-type MythTV frontend, it’s not an issue. Additionally, it is quite easy to install, and with Ubuntu, it’s quite painless. The binary-only ATI drivers have historically been harder to install and configure than the NVIDIA ones.

The good news is that since you don’t need a lot of graphics capability, the older cards should be be OK for your setup. However, this is not always true at higher resolutions. If you use a large screen you need to have a graphics card that has enough video memory to use the full resolution. Some onboard Intel cards might not -- so check first! You also need drivers that support xv -- an acceleration architecture for displaying video in the X Window System, the system that puts pictures on the screen. Some ATI cards don’t support xv, and the video will be choppy. Additionally, if your video card doesn’t support xv, then more CPU will be used during playback because the frontend will need to emulate xv with software.

Both authors have now settled for NVIDIA cards in their MythTV systems. Resolution and xv support are particularly important if you intend to play back high-definition TV.

Disk

Disk is something you will never have enough of, and it will never be as fast as you want. Storing video has traditionally been a rather demanding application, but this is not so true these days because of good compression algorithms and fast CPUs. Our main concern is disk space, not speed (external USB disks provide more than enough speed).

How Much Disk Space Do You Need?

This is an interesting question. It boils down to three factors:

• At what quality will you be recording?
• For how long do you want to keep recordings?
• Are you going to store other data (such as music, photos, or other videos) on the MythTV machine?

When doing the calculations for how much disk space to buy, remember to set aside about 10GB for the operating system. For example, a 250GB disk will get you about 234GB of formatted capacity, minus 10GB for the operating system, which leaves you with 224GB of space for recordings. It’s traditional to have the operating system installed on a separate partition on the machine’s disks, and you’ll possibly have separate partitions for /var and swap as well. These separate partitions are generally used to minimize the impact of having a partition fill up. For example, if you create many large log files in /var, having that separate will stop the rest of the machine from being adversely affected. Additionally, it gives you the flexibility to use logical disks (which we mention later) and different file system types on different partitions.

Understanding different resolutions

Throughout this book we talk about "standard definition" and "high definition" video. Apart from being marketing terms, these terms also refer to the size of each frame in the video. A high definition video has larger frames, which means that the video files are bigger because there is more data to store. Figure 1 shows the comparative size of the various video formats you are likely to encounter. Figure 1. Comparative size of various video resolutions

Recording Quality

Stewart started off thinking “as long as it’s about as good as Long Play on VHS, I’m happy” when he first built a MythTV machine. However, if he’d just bought a high-definition projector, some really nice sound gear, and an armchair with a fridge to keep the beer cool, this would not have been acceptable quality!

You might source your TV from an analog signal through a cheap TV capture card. A good analog signal can be compressed well and give you a good-quality image during playback. If you compress it more, you might still be happy with it and pleased with the disk space that you save, but the image might not be as good. Stewart has found that compression settings on a well-received analog signal that approximates a Standard Play recording on a good VCR uses about 1GB per hour of TV. A DVD is noticeably better quality than the recording; with a digital TV card, the quality is as good as DVD. With poor reception and analog, though, it can be as much as 2GB per hour of TV.

If you’re sourcing your TV from a digital TV card or any of the analog cable TV cards that support MPEG compression in hardware, then you will be receiving raw MPEG-2 streams of video. Standard-definition TV is usually 2GB to 3GB per hour. A high-definition program can use up to 7GB per hour of TV. You can record these streams without recompressing (transcoding) it, and it will look exactly like you were watching live TV through the digital tuner. However, you might choose some further compression to save disk space. You can also configure MythTV to recompress only certain programs. (For example, you might want your recordings of Law and Order to be in high definition, but you’d rather save space on Wheel of Fortune.) We discuss this in Performing Advanced TV Recording.

It’s important to note that the larger the gigabytes-per-hour rate is, the more disk bandwidth is required. This will probably be an issue only if you consider recording multiple streams at once while playing back programs.

How Long Will You Keep Recordings?

This can depend on your watching habits. Stewart has found that with the shows he records (and deleting some shows after he has watched them) with his 250GB disk, he keeps recordings for about a month before they autoexpire to make room for new ones. Michael, on the other hand, currently has 700GB of storage and has found that to be “about right” for him. You can heavily customize which recordings autoexpire first (if at all) and make programs never autoexpire. As of the 0.20 release of MythTV, Live TV recordings are now treated like regular recordings and have their own autoexpire settings. You can also at the touch of a button convert the program you were watching into a recording. Refer to Performing Advanced TV Recording and Exploring MythTV Functionality for more information.

Where Will You Store Other Data (Music, Photos,Videos) on the MythTV Machine?

Consider whether you are going to store other multimedia on the same set of disks in the MythTV machine. Here are some numbers to think about:

• Your CD collection (100MB per CD for good quality, 350MB for lossless).
• Your digital photos (largely depends on your camera and how often you take photos). This could be a few hundred megabytes or many, many gigabytes.
• Other videos. For example, think about the videos you download from Google Video, YouTube, and so on. These vary in size (and quality), and you might not want to keep them for long.

Choosing a Disk to Buy

You might also choose to buy more than one disk and set them up in a RAID or logical volume manager (LVM) configuration -- see the section entitled "Disk Layout, Logical Disks, and Meta Disks" in The_Hard_Way:_Installing_Ubuntu for more detail on those. If placing the disks in the living room, you’ll want them to be relatively quiet. Usually the manufacturer lists how much noise the drive makes in various modes of operation on the specifications page on its website. However, even the “noisy” drives can be rather quiet when in a computer case inside a cabinet with the TV on, and many disks also have options in the BIOS for speed versus noise trade-offs. Do not consider 5400rpm disks; you want the extra speed that 7200rpm gives you. Additionally, the slower disks are getting increasingly hard to find and are not any cheaper. At time of this writing, the extra cost for 10,000rpm disks isn’t worth it -- instead, it is more affordable to get two 7200rpm drives and configure them in a striped RAID setup if you’re really worried about speed.

We previously talked about how much disk space recordings might use. The general recommendation for buying a disk is to buy the biggest you can reasonably afford. There is often a sweet spot that gets you the most gigabytes per dollar. When Stewart was setting up his MythTV box, this was 250GB drives. The sweet spot is now at around 1TB drives, and by the time you read this, it will be probably higher again.

Should you buy Parallel ATA, Serial ATA, USB 2, or some new fancy connector? You are going to need an internal disk for your MythTV box, which means Parallel ATA (PATA) or Serial ATA (SATA). Stewart chose PATA because it was cheaper and he didn’t see performance as critical for him. However, the price difference between PATA and SATA is now trivial (if there is one at all), and SATA is certainly the way of the future.

Michael, on the other hand, originally decided to store most of his data on external USB 2 drives (he had one internal SATA disk and six external USB disks). However, over time he found USB disks to be quite unreliable, and has now moved to all SATA disks.

CD/DVD Reader/Writer

These days DVD writers are very cheap. There is little point in just buying a DVD reader and next to no point at all in buying just a CD-ROM drive—if you can even find one. The only debate you’re likely to have is whether you’ll get a single or dual-layer DVD writer. It all depends what you’re going to want to write to DVD and the quality at which you recorded it. Having a DVD writer in your MythTV system makes it much more like a VCR. With a VCR you can tape something from the TV and label the tape for later playback. A DVD writer lets you do the same. It makes your MythTV box similar to the DVD recorders you can buy at the local electronics store. You can read more about how to set up DVD burning with your MythTV machine in Working with DVDs.

Be careful, though; depending on where you live, you might not have the legal right to record programs from the TV and watch them later -- even with a conventional VCR (which have been commercially available for the home market for more than 30 years). Also, you might be allowed to view the recorded programs only once and not use the Rewind button. Check local laws if you’re concerned.

Video Capture Cards

Selecting a video capture card is probably the most complicated part of building your MythTV system, mainly because you have lots of choices. Choosing the right one can look daunting. The first decision you’ll have to make is deciding whether you want an analog or digital card. Because many places in the world (including the United States and Australia) plan to phase out analog broadcasts between 2006 and 2010 -- Holland did so at the end of 2006 -- digital is a safer bet. These dates are not set in stone, though, so you might find that your home country has no announced plans to turn off analog transmission or that the government has backed away from previous deadlines. The motivation for turning off the analog transmissions is clear, however; it will free up large amounts of the available broadcast spectrum for other uses. On the other hand, analog cards can be quite cheap and can require less processing power and disk space. Analog cards can also be a more sensible option with some cable TV services (for many parts of the United States this means not requiring a set-top box and setting up an IR blaster). If an analog card is being sold locally, it should support the color encoding (either PAL, NTSC, or SECAM) of your region. Most cards can easily switch between several of these with a simple software configuration change.

There are also differences in digital transmissions. There is the simple difference of standard definition versus high definition. If your TV isn’t high definition, there is little purpose in bothering to capture the high-definition signal, and you can probably safely ignore high definition (unless you plan to upgrade your TV shortly).

Finally, remember to check that your planned card is supported by Linux and by MythTV. This can be quite a subtle choice—for example, not all the Hauppauge cards are supported by Linux, but the ones that are supported work very well and are probably the most common analog cable card in use by MythTV users in the United States. You can find a matrix of the cards supported by MythTV on the MythTV wiki. Table 1 summarizes the relevant portions of that matrix at the time of this writing.

You can find a much more detailed description for each card available at the MythTV wiki page on video capture cards. However, some recommendations can make your life a lot easier, so let’s explore some recommendations for video capture cards.

Selecting an Analog Card

If you decide to select an analog tuner card, then your next step is to decide what TV sources you want to record. If you plan on recording TV that is broadcast free over the airwaves (what we refer to as free-to-air TV), then the Brooktree 878 (BT878) series is well supported, cheap, and easy to find. These cards often have an aerial input and an S-Video input, which means they can record these free-to-air sources as well as video from a set-top box such as those deployed by Foxtel in Australia and the Dish Network in the United States. To find other well supported cards, the best bet is to look for cards in stores that are listed on a “Supported Hardware” list. The Video4Linux (V4L -- the system that supports analog video capture cards on Linux) wiki maintains a list of supported cards at video4linux wiki. The wiki also has specific troubleshooting information for each driver. If you find out new information, you can also add it to the wiki so others can learn too.

For these free-to-air sources, we will focus on the BT878 cards because they are the most common, and those are the ones for which we provide installation instructions in the following sections.

If your TV is coming from analog cable, then you will need a video capture card with an analog cable input. This will be the case if you use an American cable network such as Comcast, which just provides you with a coax plug on the wall. The advantage of these cable providers is that you don’t need to use IR blasting, because the tuner on the video capture card can do the right thing. Your best choice for these analog cable providers are the Hauppauge PVR cards, although not all of them are supported by Linux, so check before you buy one. The PVR 150, PVR 250, PVR 350, and PVR 500 are all excellent choices at the time of this writing. These cards use the IVTV driver, which is also discussed later in this chapter. The only item that requires caution in selecting a Hauppauge tuner card is that the same model of card ships with different tuner modules depending on when it was manufactured, and it sometimes takes a while for the IVTV drivers to support newer tuners.

Selecting a Digital Card

If your digital source is free to air, then there is again an excellent wiki that can help you choose what card to buy because it lists supported hardware. The Digital Video Broadcast (DVB) wiki, has this list of supported hardware.

More commonly now, many small (or large) online stores will list whether the devices they are selling work with Linux. This is indeed the case for DigitalNow for example, which sells DVB-T cards in Australia. This shop is often recommended on user group mailing lists to those looking for well-supported digital capture cards in Australia.

Other Issues to Consider

Some cards support two or more tuners. These are great if you ever want to record one show after another or two shows at once. They are probably worth the extra expense because they are often cheaper than buying two cards. Adding USB capture cards can also be an option because many of them are well supported. You can read more about adding tuners to your MythTV machine in Chapter Expanding MythTV.

What the Authors Use

Now that we’ve discussed a lot of the hardware choices you have to make, what choices have we made? Often some of the best advice is from people who say, “This worked for me.” So let’s discuss what we ended up using.

Stewart’s Hardware Choices

I chose a Shuttle SN85G40, which was a current model at the time. It supports 32- and 64-bit AMD processors, giving me an upgrade path. I chose an affordable processor (the AMD Sempron 2600+), and with a cheap analog capture card and bad reception, encoding video was using a lot of CPU, and I was almost wishing for a faster one. I went the cheap option and bought only 512MB of RAM (as a single stick and have since added a 1GB stick). With the benefit of hindsight, it might have been better to buy 1GB at the start because I found that when I was watching, recording, and transcoding, some memory pressure occasionally caused recordings to drop frames.

I bought the sweet spot of 250GB of disk. I bought a 7200rpm Western Digital drive. I’ve used WD drives for several years now and have not had any problems. You will always find somebody with the opposite opinion. This is enough disk for my TV recordings. I don’t tend to keep recordings stored on the MythTV box. If I did, I’d want a lot more space.

For network connectivity, I did use a USB 802.11g network card but found it not to be too reliable. I now plug the frontend machine into a Linksys WRT-54GL running the OpenWRT firmware in “bridged client mode” so it connects to my wireless network. I happily run mythfrontend on other machines on the network. I also keep an old analog card in a machine upstairs as a remote backend. Michael also uses 802.11g wireless and has remote frontends without having any network bandwidth problems.

I used to use a WinFast TV 2000 Deluxe as a capture card—one of the cheapest analog capture cards I could find when I was first going to experiment with MythTV (and didn’t want to waste my hard-earned student dollars). I now use a WinFast DTV1000 PCI card and have been working on adding support to the Linux drivers for the new revision of a Leadtek DVB USB dongle.

Michael’s Hardware Choices

I've been through several iterations of my MythTV system. I'm currently using a Zalman 160B media center case (which included a remote control, and a LCD screen which displays the status of the system). This is a low noise case, which mostly seems to mean that it came with rubber bezels for all the screws, which reduce the amount of vibration that flows from spinning components like disks to the case.

I selected a dual core AMD X2 CPU, which was an excellent choice because it means that I can be playing back video on one CPU core while transcode jobs generally run on the other core. This means that even when the machine is doing a lot of processing, video response is still good. I have 2GB of RAM in the machine, and about 1TB of disk (in a RAID 10 configuration). My tuner is a Hauppauge PVR 350, which includes a remote control and is well supported with my analog cable TV and Linux. I also have a Hauppauge PVR 250.

My machine is connected via DVI to a Samsung 32 inch LCD television, which is effectively a large computer monitor. This is a much simpler solution than using traditional TV outputs, as they can be hard to configure.

Conclusion

In this chapter we've talked about the issues you should think about when selecting hardware for your MythTV system. Once you've selected hardware the next step is to install some software on it. There are two choices here -- you can use a Live CD to give MythTV a try, in which case you should read The Easy Way: Installing MythBuntu next. You can even install MythBuntu as an operating system if you want, which will give you a nicely configured MythTV system. If you want to use your machine for other things as well, then you're better off installing MythTV on top of standard Ubuntu, which is discussed in The Hard Way: Installing Ubuntu and The Hard Way: Installing MythTV From Source.