10 Playing other multimedia data types
Sometimes you will come across Web pages which contain multimedia data types and executable code which your browser may recognise but does not have the ability to run or display itself. To play them you need to have a 'helper' program (a 'run-time environment' or 'player') on your computer to handle the particular data. These usually display the data inside your browser window, so that it appears that the browser is in fact handling the data.
Examples of these alien data types are: Shockwave movies (created by MacroMedia Director), Java applets (browser programs created using the Java language) and high-quality digital sound.
The latest version of Acorn Internet software has been designed to accept 'plug-in' players to handle a number of different types of data you may encounter on Web pages: Java and Shockwave players are currently available for Acorn computers.
If your computer has the right player, and it has been 'seen' by the Filer, you can usually download one of these data types from the Web and play them on your computer automatically, without having to worry about how the player works.
If the multimedia file includes sound, you will need 16-bit digital audio hardware in your computer in order to be able to listen to it.
We cover two multimedia players in this chapter: !Java for playing Java applets and !Player, which plays Shockwave movies.
Java applets downloaded from the World Wide Web can be played on a RISC OS computer by !Java. !Java is the RISC OS plug-in player, or run-time environment, which is called upon by the browser when it is required to play Java applets.
!Java is supplied with the latest version of Acorn Internet software, and should be installed on your hard disc as suggested in the Release Note supplied with the software. Please take note of the minimum machine RAM requirements required to run !Java on your computer, also detailed in the Release Note.
Java is a programming language, similar in appearance to C++ but a completely new language in its own right, which has been developed for writing applications distributed over a network. Network distribution poses severe challenges for software developers because of the wide range of client computer platforms connected to the Internet: workstations with SPARC, Motorola, DEC Alpha or Intel processors, Acorns with ARM processors, PCs with Intel or PowerPC processors, Macintoshes with Motorola or PowerPC processors. For each one of these would a program have to be separately compiled to make sure that it would run once it had been downloaded.
Java is 'platform independent'; that is to say that the same applet will run on any computer with a Java player connected to the Internet. How is this possible? Well, every Java applet is part-compiled into bytecode for a single target computer, the 'Java Virtual Machine'. This target computer, as its name implies, does not exist in reality; it is just a standard to which all Java code must adhere. Java is an interpreted language, so each computer on the Internet which wants to run a Java applet must have a standard Java interpreter (standard as far as its interface with the applet is concerned). The interpreter will always run the Java code in the same way, irrespective of the machine on which it resides. In this way only the Java interpreter has to be ported once to each type of computer, not every applet you want to run on it.
Downloading data from the Internet is relatively secure - data alone cannot introduce viruses into your computer. Executable code is another matter: you will naturally be concerned about downloading programs from a source about which you may know little. The authors of Java have addressed this concern by making Java code protect the integrity of your computer in the following ways:
The operation of !Java is transparent to the user. When you click on a Java applet on a Web page, as long as it can find it (see the Release Note on where to install plug-ins), the Acorn Internet software plug-in interface will call !Java to handle the applet, opening a window in your browser. Depending on the applet you have loaded, additional controls for the applet may also appear.
The presence of !Java is indicated by its icon appearing on your icon bar.
!Java quits automatically a short time after you quit the last Java applet. The delay may be altered by editing the !Boot file. When !Java quits, it gives back all the memory it was using.
You can quit !Java manually by choosing Quit from the !Java icon bar menu.
!Shockwave is the plug-in RISC OS application which is summoned automatically by Acorn Internet software when it is required to play Shockwave movies. At present !Shockwave will only play movies developed using Macromedia Director 4.
!Shockwave is supplied with the latest version of Acorn Internet software, and should be installed on your hard disc as suggested in the Release Note supplied with the software. Please take note of the minimum machine RAM requirements required to run !Shockwave on your computer, also detailed in the Release Note.
Shockwave movies are produced by the multimedia authoring application Macromedia Director, an application widely used for presentations, home shopping, interactive training, cartoon animations and sales kiosks.
They include text and graphics, animations, digital video, fades, dissolves and other effects, as well as sound tracks.
Shockwave movies may be authored on Macintosh or Windows platforms, but both versions may be played by !Shockwave. Mac peculiarities, such Shadow and Outline fonts, are replaced if necessary by an equivalent RISC OS font.
The operation of !Shockwave is transparent to the user. When you click on a Shockwave movie on a Web page, as long as it can find it (see the Release Note on where to install plug-ins), the Acorn Internet software plug-in interface will call !Shockwave to play the movie, opening a window in your browser. The movie may bring its own play controls with it.
The presence of !Shockwave is indicated by its icon appearing on your icon bar.
!Shockwave quits automatically a short time after you quit the last Shockwave movie. The actual delay be altered by editing the Shockwave !Run file. When !Shockwave quits, it returns all the memory it was using.
You can also quit !Shockwave manually by choosing Quit from the !Shockwave icon bar menu.