Browser requirements

If I were to make a report on paper, I could send the actual paper print-out to the person I wanted to read it. I would not have to worry much about what it would look like for him/her, since it was the very paper I myself had had in my hand, that he/she would have gotten.

If I were to make a report on a video tape, it would still be fairly simple, but I would have to make sure, that that person were able to view the video tape format I had used, e.g. Super-VHS PAL. And of course, it would be absolutely necessary that the person had a VCR in the first place.

Now that I am making a report as a multimedia document on the Web, what then? As a first prerequisite, the person should have a Web browser (such as Netscape), running on a machine with access to the Net. In more details, the browser requirements for this multimedia report are:

Ability to show the different occurring content types:

As discussed earlier, there are several different ``classes'' of content types, e.g. still images, movies, and 3D scenes, and within these classes there are several different ``formats''. These latter each have a distinct so-called MIME type. When a Web server sends some data (e.g. the contents of a GIF file), it also sends the MIME type, so that the Web browser (e.g. Netscape) knows what kind of data it is getting. The Web browser then has a table (the mailcap), that specifies what to do with a number of different MIME types; it could either handle it itself, or it could send it to an external viewer.

Here is an example of all the different MIME types that I use in this Web exhibition. Try to click on it and see what happens. If your browser just lets you save the file without displaying it, help might be found further down. Note, that I will explain later what these files show.

text/plain:

Text, plain

text/html:

Text, HTML (that is what you are reading right now ;-)

image/gif:

Still image, GIF

video/mpeg:

Movie, MPEG (here: MPEG-1 video bitstream)

video/quicktime:

Movie, QuickTime (here: Animation coded)

image/gif:

Movie, Animated GIF

application/x-inventor:

3D Scene, Inventor

x-world/x-vrml:

3D Scene, VRML

application/postscript:

Page description language, PostScript

Ability to show the HTML markup used:

I have used HTML version 2.2, that have tags for making tables. If you see a nicely formatted 3 by 3 table right below this, your browser understands these tags:

type style

smart red short

rather silly puce tall

(courtesy Lamport 1986 ;-)

Ability to make interactive forms:

In this project I have also used interactive forms. For these, the browser needs to render the associated HTML tags correctly, accept input from the user, and send it in the right way to the Web server. An example of a form follows here. It will return an HTML document telling you what value you submitted.

input a number!

or

Ability to decompress compressed files:

I have often compressed Inventor and VRML files using gzip, since their size is reduced a factor of 5 that way. Here is a gzip'ed Inventor file.

If all of the above worked for you, you do not have to read through the rest of this section!

So, what kind of setup fulfills all of the above requirements? To start with the three last ones (tables, forms, and gzip): just get Netscape version 2 or later. I have been running version 2.02 myself.

To be able to view all the above mentioned MIME types, you have to:

• Have an external viewer for those MIME types which your Web browser cannot handle itself (Netscape has built-in viewers for plain text, HTML, GIF, and animated GIF).
• Have your Web browser configured to actually use these external viewers. For Netscape, this is done through the mailcap file. There are actually two: a system-wide and a personal; follow the menu chain Options General Preferences... Helpers to see where they are located (typically /usr/local/lib/netscape/mailcap and ~/.mailcap).

If you are running on a Silicon Graphics computer like I am, you could use the following mailcap:

video/mpeg; mpeg_play %s >/dev/null 2>&1; \
        description="MPEG Movie"; \
        x11-bitmap="/usr/lib/Zmail/bitmaps/movie.xbm"

video/quicktime; movieplayer -nofork %s >/dev/null 2>&1; \
        compose=moviemaker %s; \
        description="QuickTime Movie"; \
        x11-bitmap="/usr/lib/Zmail/bitmaps/movie.xbm"

application/x-inventor; ivview %s >/dev/null 2>&1

x-world/x-vrml;  /usr/local/bin/webspace -remote %s -URL %u ; \
        description="VRML document"

application/postscript; ghostview %s; \
        description="PostScript Language";

The syntax is actually quite simple, it is ``MIME_type; viewer %s'', where %s will be substituted by the name of the temporary file containing the data. Netscape spawns external viewers using the Bourne Shell (/bin/sh), and ``>/dev/null 2>&1'' is the syntax for throwing away standard output and standard error, so that one does not have to click ``OK'' on all the messages like ``could not allocate whatever color'', or ``played movie at foo frames per second''.

Note, that the MIME types text/plain, text/html, and image/gif are not mentioned, and therefore they will be handled by Netscape itself. This is important, since an external GIF viewer might not be able to view animated GIFs - this is the case for xv and imgview. Note, that both the system-wide and your personal mailcap file has not to map image/gif to anything for this to work.

About the viewers I am using, and possible alternatives:

• mpeg_play: public domain MPEG player.
  Alternative for playing MPEG movies: Not XAnim, since it can only play the I frames, not the B and P frames (for what I, B and P frames are, see e.g. Patel, Smith, & Rowe (1993)).
• movieplayer: A Silicon Graphics specific program that plays among other things QuickTime movies. QuickTime movies using the Animation coding does not require a license, while those using Cinepak coding does. Please note, that you have to chose Play Every Frame in the Options menu before you press Play to get the intended result.
  Alternative for playing QuickTime movies: XAnim.
• ivview: A Silicon Graphics specific program that views / renders Inventor files.
  Alternative for viewing Inventor files: Nothing I know of. But since in this context Inventor and VRML are virtually the same, as long as you can view the latter, you are OK.
• webspace: A Silicon Graphics specific program (I think) that views / renders VRML files.
  Alternatives for viewing VRML files: VRweb (here or here); also check out what Yahoo has to say on VRML browsers.
• ghostview: A public domain PostScript viewer. Silicon Graphics users can also use xpsview.

A final comment is about speed, e.g. the speed with which you can play a movie. Here at the Observatory, we have a number of Silicon Graphics Indys with typically 32 Mbytes of RAM and a 100 MHz R4000 CPU. They run as X-terminals, and the typical user will via them log in to a computer with more RAM and a faster CPU (say, an R8000). However, for playing movies, I have found a speed factor of 4-25 in favor of the Indy! Therefore, I advise you to run Netscape and thus the movie viewers locally, if you have the same type of computer setup as we do, or even better, to make the comparison yourself.