2004.08_Desktopia-Xvidcap-Produce Tutorial Films with Ease.pdf

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Airtime for Programs

At times, it can be quite difficult to

describe an application’s functions in

words. A screenshot can help. If you

need more than just a still picture,

xvidcap can provide the answer. Now

it is possible to make teaching aids

that use recorded animations of you

actually using the software so others

can see exactly what you are doing.

BY ANDREA MÜLLER

desktop for demonstration or

training purposes has never been

an easy task. Although several dozen

programs compete for the favor of users

that produce documentation, none of

them is a real movie mogul. Enter xvid-

cap [1] by Rasca Gmelch. The program,

which is now maintained and developed

by Karl H. Beckers, is tailor-made for cre-

ating on-screen demos. It can create

images or MPEG files of user-definable

desktop areas, and is thus perfectly

suited to pointing the way through

nested menu structures.

( Woody ), and another for Debian Test-

ing, a.k.a Sarge .

Users of other distros will need to

compile xvidcap themselves. This

assumes that you have installed the

developer packages for libpng , libjpeg ,

and XFree86 on your system. Just follow

the standard procedure: ./configure ;

make ; su -c make install to build xvid-

cap and install the program in the

directory structure below /usr/local . As

root is the only user with write permis-

sions for this level, you may need to

enter su -c to temporarily assume root

privileges for the make install step.

xvidcap relies on the ffmpeg [2] pro-

gram to create video clips. If this is not

installed on your system, your version of

xvidcap will still be able to create screen-

shots, but will not handle videos. If your

distribution does not include the ffmpeg

package, you will need to build the ffm-

peg version included with the xvidcap

distribution. To do so, add the —with-

forced-embedded-ffmpeg parameter to

the ./configure command to create an

xvidcap with embedded ffmpeg support,

or change to the ffmpeg subdirectory

before compiling xvidcap . Enter ./config-

ure ; make ; su -c make install in this

directory to create the ffmpeg encoder,

and the ffplay player, and then type

make install to copy these tools to

/usr/local/bin . The advantage of this

approach is that it allows you to use ffm-

peg and ffplay independently of xvidcap ,

which the embedded variant does not

allow you to do.

The —with-gtk2 ./configure option is

also interesting if you are building the

program yourself, as it creates a program

called gvidcap . In contrast to the origi-

nal, gvidcap has a modern gtk-2 GUI

which perfectly matches the current

Gnome desktop.

The Director’s New Tools

Before you take your first steps as an on-

screen movie director, you will obviously

need to install the program. This is easy

enough for users whose distributions

support the RPM or Debian packages

from the xvidcap homepage. The RPM

provided by the program developer sup-

ports Suse Linux 9.0 and Red Hat 9.0,

among others. There are two packages

for Debian: one for the stable version

Figure 1: The desktop movie creator xvidcap.

Figure 2: The gtk-2 variant has a more modern

look than the original.

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xvidcap

R ecording program steps from the

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Figure 3: Use this dialog to specify the output for-

mat and the output file name.

The Script

To launch the new tool installed in the

last step, type

xvidcap &

or enter

gvidcap &

Figure 4: MPlayer playing a video about email readers created with xvidcap.

to launch the gtk-2 version. The control

elements for xvidcap (see Figure 1) and

gvidcap (see Figure 2) are organized in

exactly the same way. This has an upside

and a downside. The original version

may look dull, but it is certainly more

stable and more highly configurable than

the more modern version. Stability, con-

figurability, and the fact that both

interfaces are similar, are what made us

decide to concentrate on xvidcap in this

article.

When you launch the program, it dis-

plays a red frame about the size of a

credit card to indicate the recording area.

The frame moves with the program win-

dow. To prevent this, you can click on

the x button to detach the frame from the

rest of the application. As the default

size is too small for anything but the tini-

est of tools, you will want to define the

desktop area that you are interested in

recording before you do anything else.

Click on the cross-hair in the toolbar to

change the mouse cursor to a cross-hair.

You can then either hold down the left

mouse button and drag the mouse to

define an area, or click on a window,

assuming that you are only interested in

this window’s content. If you select a

window, the video clip will not include

that window’s title bar.

After selecting your location, the next

step is to define a few parameters, such

as the output format. [Alt-O] (or [Ctrl-P]

for gvidcap ) will open the configuration

dialog shown in Figure 3.

First of all, set the value for Max

Frames to 0, as xvidcap has a default

restriction of 30 images. A value of 0

removes this limit, allowing you to create

video clips of any length. Use the Frames

per Second (FPS) box to specify the num-

ber of images per second xvidcap will

capture. The default is 25 – don’t be con-

fused by the way this is displayed

( 25.000000 ). If you need to create

MPEG 1 or MPEG4 video clips, check out

the xvidcap manpage (option —fps ) for

the required frames per second values.

For example, 25 and 50 are valid frame

rates for MPEG1, whereas MPEG4 can

use values between 7.5 and 30 . If you

enter an invalid value, your video clips

will either run too fast, or too slow.

Enter the video codec (e.g. MPEG4)

into the codec field. This defaults to

MPEG1 , but you may want to change this

to MPEG4 for enhanced recording qual-

ity. The resolution of the MPEG1 videos

we created was so poor that we were

unable to decipher some of the menus at

times.

Video or Single Image?

You still need to type the output file

name into the File pattern box. If you

leave the default, frm-%04d.xwd , xvid-

cap will not create a video, but instead

generate single xwd ( xw indow dump )

formatted files in the directory where

you launched the program. The %04d

string adds a serial number to the image

file name, creating the files frm-

0000.xwd through frm-9999.xwd . The

percent sign indicates formatting infor-

mation: 04d ( d for decimal) specifies the

number of digits. If your demo will have

more than 10,000 images, simply change

the value for File pattern to frm-

%05d.xwd , or even frm-%06d.xwd . You

can modify both the base file name ( frm )

GLOSSARY

gtk-2: : The Gimp Toolkit with the major ver-

sion 2. This graphical library provides

developers with ready-made widgets for GUI-

based applications, such as radio buttons,

dialog boxes, and input fields. Besides the

Gnome desktop version 2.0 or later, the new

Gimp is also based on gtk-2.

MPEG: Abbreviation for Motion Pictures

Expert Group. This group, which comprises

enterprises and universities, standardized

compression techniques for video formats.

MPEG encoding attempts to describe as many

image segments as possible by specifying

how they differ from the previous image; this

in turn allows for smaller file sizes.

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and the output format. xvidcap can also

create JPEG or PNG files. Single images

are useful if you need to edit the results

or if you are trying to get your hands on

a screenshot that programs like ksnap-

shot can not deliver, such as an error

message that pops up on your screen

and immediately disappears.

To create a video directly, change the

entry in File pattern to any file name

using mpeg as the extension, for example

programdemo.mpeg . To avoid modifying

the options each time you use the pro-

gram, click Save . This tells xvidcap to

store your settings in the .xvidcap.scf file

below your home directory. The gtk-2

counterpart, gvidcap , reads its defaults

from the same file. In other words, any

changes you make in one program will

immediately take effect in the other.

Deleting ~/.xvidcap.scf will restore the

program defaults.

images to a MPEG1 video clip. The fol-

lowing line

xvidcap*mkVideoCommand:ffmpeg U

-i %s video.mpeg

Figure 5: xvidcap uses Display to open individual

images. Display has a number of image manipu-

lation features. The Enhance menu has options

for modifying the brightness, gamma values and

saturation.

in ~/.Xdefaults tells xvidcap to call ffm-

peg when you select Make Video . For

this to work, you need the ffmpeg pro-

gram proper: you can not use the

xvidcap embedded variant. xvidcap

replaces the %s string with the name

pattern used by the individual image

files – this was pic%04d.png in our

example. As ffmpeg recognizes this nam-

ing convention, it can convert files with

names such as pic0000.png , pic0001.png

one by one and store the result in the

output file, video.mpeg , below the cur-

rent directory.

There is a pitfall to watch out for when

using ffmpeg to generate a video from

individual image files. The encoder can

not handle the xwd files that xvidcap cre-

ates by default. ffmpeg uses the

following graphics formats: pnm , pam ,

pgmyuv , yuv , png , jpeg , and gif . The

PNG format is a good choice when grab-

bing screenshots with xvidcap . To select

the PNG format, select the PNG file

extension as the File pattern in the xvid-

cap options menu.

The quickest way to success for ama-

teur screen directors is to tell xvidcap to

create video output, and leave individual

image processing to users who are unsat-

isfied with “run-of-the-mill” video clips,

and want to modify the raw material

before generating a video clip.

Take One, Action!

Click the button with the red dot to start

recording the desktop area within the red

frame. After demonstrating the software

aspects you are interested in, click on the

button with the black square to stop

recording. You can use a player like

MPlayer (see Figure 4) to play back your

demo to an appreciative audience. To

keep things simple, you can opt to use

the ffplay command-line player supplied

with ffmpeg . The following command

launches the tool

with the pencil image on the right

opens the current image in display , the

image viewer from the ImageMagick

package. You can then click on the image

window to pop up a menu with a num-

ber of image manipulation functions (see

Figure 5) such as color ( Enhance ) and

size manipulation, or rotation ( Tr ans-

form ) features, and a number of Effects

( F/X ).

The button with the filmstrip calls

animate , another tool from the

ImageMagick collection. As the name

suggests, animate creates and plays an

animation made up of the individual

image files. Avoid using this option with

collections of more than 400 images.

Feeding too much material to animate

will bring even the most powerful system

to its knees.

ffplay videodemo.mpeg

■

Pressing [q] quits the show.

After creating a series of images, you

can click on the buttons with the left

or right arrows to flip through the indi-

vidual images. Clicking on the button

INFO

[1] xvidcap: http://sourceforge.net/projects/

xvidcap

[2] ffmpeg: http://ffmpeg.sourceforge.net/

From Single Images to Video

Clips

File | Make Video converts your images

to a video clip. xvidcap parses the

~/.Xdefaults to discover what program

it should use for this task. This is where

the defaults for the graphical programs

are stored. This said, gvidcap does not

honor the assignments in ~/.Xdefaults ,

so the conversion command will only

apply to xvidcap . Let’s assume that you

have a collection of PNG-formatted

images, with names based on a format

string such as pic%04d.png , and that

you want to use ffmpeg to convert these

GLOSSARY

After nearly two

years as an indepen-

dent journalist,

Andrea Mueller has

now taken up a new

editorial position at

Linux New Media AG.

When she is not taking care of articles,

or wrapping packages for the

EasyLinux download area, Andrea

looks beyond Linux and is involved

with other operating systems such as

QNX, BeOS and NetBSD.

ImageMagick: A collection of ten image

manipulation tools. As most of these tools

are command line based, ImageMagick is the

perfect choice for scripting image conversion

and manipulation jobs.

~/.Xdefaults: This is where users can define

preferences for GUI-based programs, such as

the background color or the font. To find out

which preferences an application can use,

you need to check the manpage for that

application. Current KDE and Gnome applica-

tions typically ignore the settings in

~/.Xdefaults.

August 2004

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