Hardware Hacking Projects for Geeks

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Chapter 7, How to Build a Digital Video Recorder

You will probably want a slim case for the parts as well. A complete PC may

even be available from eBay or a local computer shop with all of these parts

already installed. The HP desktop PC case and system pictured in Figure 7-1

was upgraded with a new hard drive and worked well for this project.

Put the PC together and test it out with a standard VGA monitor before pro-

ceeding. You can install any operating system you like for testing because it

will be replaced later.

Software Setup Instructions

The first thing you need to do is install a Mandrake Linux Version 8.2 pack-

age on your computer. Next, you will install a number of Video4Linux driv-

ers and software packages. Finally, you will test out your system.

1. Install Mandrake Linux Version 8.2

Download or purchase a copy of Mandrake Linux 8.2 and install it on the

PC you’ve constructed. The software should recognize all of the hardware.

You will need to use a standard monitor when installing the software

because it requires at least 800 by 600 resolution.

Figure 7-1: Home-built PVR in place

Which Version of

Linux?

There are a number of Linux pack-

ages available today that will prob-

ably work with this project. Mandrake

8.2 was used and tested because it

included XAWTV (X Athena Widget

set for TV) and drivers for most video

capture cards. If your Linux package

does not include drivers for your

video capture card and the XAWTV

video record/playback utilities, you

will need to obtain and load them

yourself.

Software Setup Instructions

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132

Part II: Advanced Hacks, Tools, and Techniques

2. Configure the system

1. Start by creating a login account. A login of tv with no password will

work well.

2. Create a directory to store your recorded programs. A directory called

“shows” should work.

3. Add these lines to the /etc/modules.conf file:

pre-install videodev modprobe -k tuner type=2

options bttv gbuffers=2 card=16 radio=1 fieldnr=1

4. Create a script that triggers video recording. Below is an example script

called rec that you can locate in /home/tv:

#!/bin/bash

if test -z "$2"; then echo "usage: channel lengthoftime"; exit; fi

f=shows/'date +%y%m%d-%a-%H_%M'

echo $f >> /tmp/TV_rec.err

echo “ Recording channel $1 ($2) at 'date'" >> /tmp/TV_rec.status

killall -9 xine 2>> /tmp/TV_rec.err

killall -9 mplayer 2>> /tmp/TV_rec.err

killall -9 xawtv 2>> /tmp/TV_rec.err

v4lctl setchannel $1 2>> /tmp/TV_rec.err

v4lctl volume 100 2>> /tmp/TV_rec.err

mencoder -tv on:driver=v4l:device=/dev/video0:norm=NTSC:

width=320:height=240 -oac copy -ovc lavc -lavcopts

vcodec=mpeg4:vbitrate=800 -vop pp=lb -endpos $2 -o $f.avi 2> /dev/

null > /dev/null

echo " Ended recording channel $1 at 'date'" >> /tmp/TV_

rec.status

If you wish the files to be VCD-compatible, remove the mencoder line

and replace it with:

streamer -n ntsc -q -t $2 -s 320x240 -r 20 -o $f.avi -f jpeg -j

86 -F stereo 2>> tmp/TV_rec.err

The mencoder format allows a very high frame rate (up to 27 fps on the

system tested).

To operate the script, pass it the following arguments: the channel

number, and a number of minutes and seconds to record. It will then

record a file in the format “YYMMDD-day-HH_MM.avi” (e.g.,

021008-

Tue-19_00.avi

) in the shows subdirectory.

This script does a lot of things that aren’t really crucial. All the output is

redirected to a log file for debugging purposes. It also writes to a status

file before and after the recording.

If you are running other programs and your Linux PVR is not a dedi-

cated machine, the

killall -9 command is a bit harsh. You can replace

this with a simple

kill command instead or add a series of escalating

termination commands to the script.

What Is a VCD?

VCD stands for video CD. VCDs use a

file format that can be burned onto

a standard compact disc and played

back on most DVD players. For details

on how to go about this, check out

http://sourceforge.net/projects/vcd-

master/.

Card ID

If you have chosen to use a different

capture card, the “card=16” in this

code should be changed to the card

you are using. Check this web site for

card ID details: http://sdb.suse.de/en/

sdb/html/cg_wintv.html.

Software Setup Instructions

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