Hack38.Play DVDs with Your in-Car Computer


Hack 38. Play DVDs with Your in-Car Computer

The most obvious reason to install video in the car is so your passengers can watch movies, and with a computer, the in-car DVD experience can be even better.

DVD entertainment is the major driver of in-car screen sales. In-car video entertainment was once rare, but now you can purchase a DVD player and two headrest screens for the rear passengers for under $300.

But this cheap solution doesn't give you the best DVD experience possible. In-car portable DVD players are limited. Most of them include only stereo sound, not surround sound (Pyle, at http://www.pyleaudio.com, and Phoenix Gold, at http://www.phoenixgold.com, are notable exceptions), and most of them are limited to composite video output, which is the lowest acceptable video quality.

A modern personal computer is a much more powerful DVD player. For about $50 you can get a full-featured software DVD player that does progressive scan conversion (a method of enhancing the visual quality of DVD video for flat screens and computer monitors), offers surround sound, and can be set to play DVDs from any region (U.S., Europe, etc.). Computer-based DVD players can drive high-resolution screens at the full DVD resolution of 720 x 480, and even higher on larger flat screens.

3.17.1. Locating Your DVD Drive

There are several approaches to getting DVD drives into a car. Many in-car computer enclosures have an integrated CD/DVD drive, either tray-or slot-loading. However, most computers are too large to fit in the dashboard, or even under the seat.

If you have a large vehicle with a center console between the driver and passenger seats, you may be able to hide your computer in that unit, mounting the DVD drive so that it can be accessed by the front or rear passengers.

However, the standard location for an optical drive in cars is in the middle of the dashboard. Thus, for the driver's convenience, you want a small drive that you can install seamlessly in the dashboard alongside any existing CD drive. Figure 3-20 shows one of the many slim-line CD/DVD enclosures that are excellent for this purpose. Several models exist that provide both USB and FireWire connectors, are less than 1" tall, and can accommodate any laptop-sized DVD drive. Although a conventional 5.25" CD drive enclosure (also pictured in Figure 3-20) could fit in a single-DINslot, your dashboard would look like the front of a PC casenot a very attractive install. Instead, you should mount a slot-loading, laptop-sized optical drive (or a Mac Mini [Hack #54]) using an existing or fabricated horizontal slot in the dashboard for a very stealth install.

Figure 3-20. An internal DVD drive, a laptop DVD drive, and a Mac Mini


3.17.2. Connecting Your DVD Drive

The easiest approach is to mount your DVD drive externally from the computer, so that your computer can be located wherever you want. If you have a full-sized computer installed in the trunk, you can use three-meter cables to connect it to your DVD drive in the front area. But what interface should you use?

Since it's likely you'll want USB connectors near the dashboard [Hack #51] anyway, you may simply want to connect a USB hub for your in-dash DVD player. This install looks best if you cleanly flush-mount the USB adapter, but it looks bad to have the USB cable from the DVD drive looping out of the dash to plug into the front of the hub. So, for a clean install, you need to either use two USB hubs, with one facing inwards for a connection to the DVD drive, or run a pair of USB cables from the computer up to the front of the car.

Another consideration with USB is power. Optical drives take around 600 800 mA of power at 5V. This is above the 500-mA limit provided by USB 2.0 hubs. I've personally tried half a dozen USB hubs to no availthey purposely limit the power. Thus, the DVD drive has to be separately powered, requiring another 12V-to-5V adapter. These are cheap and easy to findat Radio Shack and any auto shop, you can find cigarette lighter adapters that adapt 12V down to 9V, 6V, 3V, or 1.5V with a switch. And a company called ZIP-LINQ (http://www.ziplinq.com) even makes a unit that is basically a 12V-to-USB adapter.

It's important to note that these units may not provide the clean, regulated 5V power your DVD drive needs and may be designed for more robust equipment. If you want a safer power environment for your DVD drive, use a regulated adapter (Google "12V to 5V DC-to-DC power supply").

With smaller motherboards, such as the popular VIA EPIA models, the USB power output isn't enough to power an external DVD drive by the wire itself. However, if you have a larger computer and a hearty power supply, you may be able to get away with a single USB cable that can power the device.

The motivation for having only a single wire is more than just to reduce clutter. A bus-powered device (which gets its power from the cable, not a separate power supply) ensures that the DVD drive is on only when the computer is on, and avoids synchronization problems when the DVD drive is suddenly powered off (e.g., when you pull the key out of the ignition) when the computer is still on or, even worse, reading from the disk (which won't hurt the player but will probably crash your operating system). Another benefit of bus power is that you don't have to install yet another power adapter in your dash.

The most successful bus power approach is to use FireWire cables (the larger, 6-pin version). FireWire has very solid power characteristics and was designed to drive fairly thirsty external devices. The maximum rated length of a FireWire cable is about three meters, and in practice they work at longer distances than that. FireWire cables are nicely shielded, and I've purchased a 15-foot cable at Fry's Electronics for around $12.

FireWire is also nicely compatible with the 12V in cars. Similar to the 12V-to-5V cigarette lighter adapter mentioned earlier, the older FireWire iPod rechargers can be used to power FireWire devices. FireWire devices have additional circuitry to deal with a range of input voltages, and they aren't likely to suddenly give up on life if the voltage fluctuates.

There's one more reason to use bus power. Many of the power adapters for external devices are barrel plugs . These cylindrical plugs can pull or fall out easily, requiring you to take your dashboard apart to get the DVD player working again. USB and FireWire connectors plug in more firmly and are less likely to pop out after installation.

3.17.3. Running the Right Software

It wasn't until computer processors reached 400 MHz that PCs had enough power to decode DVD MPEG-2 video using software. Modern processors with speeds greater than 1 GHz have no problems decoding DVD video, but the multitasking features of computers can still cause jitters and quality problems when the PC has other work to do, such as driving multiple monitors or accessing networks.

There are a number of DVD programs and hardware solutions available for PCs. WinDVD (http://www.windvd.com) and PowerDVD (http://www.gocyberlink.com) are two mainstream Windows applications, both of which play DVDs with high quality on any GHz-class machine. They each come as $15 add-ins to Windows Media Player, or you can buy the full-fledged versions of the programs for $5070, depending on which additional features you choose (such as 5.1 surround sound).

The very popular, compact VIA EPIA motherboards are used extensively for in-car computing. They are low power, low heat, and run an Intel-compatible processor at speeds around 1 GHz. However, these CPUs have lower floating-point performance than real Pentiums, and thus DVD playback taxes their processors. While they advertise built-in MPEG-2 decoding hardware assistance, the only DVD player that implements this is a closed-source version of Linux DVD software (a bad mix, if you ask me). PowerDVD and WinDVD seem to run fine on these machines (not the 600-MHz versions, but the 1GHz and above models), but it's a shame that they don't use the built-in hardware support.

I'd have to say my favorite DVD player is MPlayer (http://www.mplayerhq.hu), which runs on Linux, Windows, and Mac OS X. One of the features I like most about it is that it runs from a command line from which you can configure all sorts of features, such as which screen to start playback on and which track or scene in the movie to start with. This allows you to start playing the movie on a DVD instantly, without going through all the trailers and the menu system. This also makes it safer for the driverif you can hit one button on your touchscreen and play the movie, that's better than having to hit Play, wait for a menu, and then hit Play again.

3.17.4. Putting It Together

My own car-computer setup is designed so that I can put in a DVD and start it playing in the front seat without having to watch the video. I remain in control of the media, but those in the back seat get to watch. I can also choose whether to pump the DVD sound through the car's speakers or let the back-seat passengers listen on their own headphones.

To accomplish this, I use the dual monitor setup available on the VIA EPIA boards. They have a VGA output (which I've connected to my dash-mounted VGA touchscreen) and both a composite and an S-Video output.

I run one of these outputs to the rear monitor (I only have one headrest monitor, but the output could be split and amplified to any number of other screens) and the other to the composite input of my VGA touchscreen.

While I'm driving, I leave my software running on the primary (VGA touchscreen) monitor. If I insert a DVD, I have my software configured to play the DVD on the second monitor (the composite output).

If I want to watch too (i.e., while stopped or to quickly check what's playing), I press the SOURCE button on the VGA touchscreen and switch from VGA to the first AUX video input. Then I switch back to my VGA signal when I want to run the primary desktop on my PC.

Once you get DVD working well in the car, you may realize that you have four or more speakers, yet you're only playing back a stereo soundtrack. "Put Multi-Channel DVD Surround Sound in Your Car" [Hack #39] tells you how to correct this shortcoming.



    Car PC Hacks
    Car PC Hacks
    ISBN: 0596008716
    EAN: 2147483647
    Year: 2005
    Pages: 131

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