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From: Markus Gebhard <ukgh@rz.uni-karlsruhe.de>
Newsgroups: alt.ascii-art
Subject: Re: Jave Movieplayer suggestions
Date: Thu, 21 Jun 2001 15:02:28 +0200
Organization: University of Karlsruhe, Germany
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Hi,

> As usual .. Tons of suggestions
> Posted here in this group to be discussed.

Great. I want to make some statements about the compression:

> 4) [Moviecompression)
> Store each frame as only the differences from another frame. It doesn't have to
> be the previous frame (though this is easier to implement), for optimum
> compression it should be based on the frame in the movie that remsembles it the
> most.

I have done lots of testing now and the result is clear to me: I will
not add this kind of differential compression to the jmov-format.

Here is what I have done:

I have written a converter to convert the star wars asciimation
(http://www.asciimation.co.nz/) into the jmov format. The asciimation
format is very simple, because it stores all frames in a compressed text
file. Each frame has a number telling for how long it has to be
displayed (how often it has to be repeated when using 15fps). (Note: the
other things discussed about differences of frames in the
asciimation-faq do not apply to the player, just to the way the
animation has been created)

To handle this multiplicity in jmov I have added a new option to the
jmov format. The jmov-command for a new frame ("J: ...") without
compressed content code attached will be handled just as if the content
did not change since the last frame.

Now here are the results from my tests:
              +------------------+-------------------+
              |       raw        |       ZIPed       |
(13934frames) |Bytes/            | Bytes/            |
              |  Bytes per frame |   Bytes per frame |
+-------------+------------------+-------------------+
|  original   |     1688323/     |      72326/       |
| asciimation |      121.1       |        5.2        |
+-------------+------------------+-------------------+
|    JMOV     |     954966/      |      65523/       |
|             |       68.5       |        4.7        |
+-------------+------------------+-------------------+
|    JMOV     |     369507/      |      51004/       |
|diffenential |       26.5       |        3.7        |
+-------------+------------------+-------------------+

So supporting differential compression is 22% better (after ZIP
compression) than compressing w/o looking at the differences. On the
other hand it makes it much more difficult to write software for the
jmov format.

So I do not want to add support for this kind of compression.
BTW: I think 4.7Bytes per frame is very good - the best ascii animation
compression I have seen in the www (consider the JavaScript animations).

But if you insist on getting better compression rates have a look at
AsciiPacker.java in the Jave Player package. There is only one (real)
compression algorithm in there for compressing a single frame - and it
is not a very good one either. Today I have tested two ideas for
improving it but the result always was the same: the raw jmov file
becomes slightly smaller, but the ZIPed one grows...

> 7) [colourchange]
> A supported command to change output colours.

Support for that will be available in the next release.

Markus

PS: It is an open source project - everybody is invited to improve the
player :)