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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I have just released onto SqueakMap a
“pure” Smalltalk port of the Ogg-Vorbis decoder from Xiph.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>It is VERY slow, very buggy and the code is so ugly
that it would definitely win the “Ugliest Code Competition”.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I have had a compulsion to write an Ogg decoder and
so I took the hardest, slowest way I possibly could because I am lazy
(confused? Me too).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I could have linked the libraries via a plugin and
saved myself a huge amount of work, but I convinced myself that a
“pure” codec would be so cool.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I think it is definitely useable after much
refactoring and optimisation. I have very little experience in Smalltalk, I use
it as a hobby and so my knowledge of the correct structure for code like the
Ogg stuff is very limited.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I am not going to have much time to spend on the code
for at least a month probably two so rather than the code gather dust, I
thought I would put it out so I can get some suggestions on the best way of
tiding up the code. Great learning experience for me.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>The code is a mixture of the documented algorithm and
the C code for the reference codec. It is missing many things (error checking
being the main one) and will probably not decode all types of Ogg files. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I think Exceptions can be used for the error handling
as sometimes reaching the end of a packet unexpectedly is fatal and sometimes
its ok (you just return what you had decoded to that point). Is that right? Or
is there something better (or more standard)?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>There are a lot of loops; I guess you could say a lot
of “passes” over the data to recover the audio. There is probably
not a lot to be done to reduce the number of passes but a lot could be done to
optimise each step individually. I must admit I only understand the algorithm a
little bit and sections like the MDCT (Modified Discrete Cosine Transform) I
have had to rip almost straight from the C code. I looked at the code for ages
and could not figure out any way to make that code better/easy to understand. I
don’t have enough of a maths background to understand the original
equation for the transform and come up with a better way of doing it in
Smalltalk.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>Xiph released a version of OggVorbis called Tremour
which is integer only (mainly for embedded devices). Would it be faster to
modify the code to use integers only?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>Obviously making sections of the code a plugin would
be a good idea. One of reasons I wrote the whole thing in Smalltalk was so it
would be easy to use Slang instead. I have left most of the loops as zero based
and most ‘at:’ statements have “+1” added separately to
make them easier to remove. I haven’t had the time to really get into
Slang and plugins so any advice would be appreciated! :) What is the best
class to subclass from? How do I do a plugin that doesn’t need any
external code? For sections like the MDCT can I just put a huge chunk of C code
in a method? How do I pass an array of floats?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I did try a little bit while I was coding but after
my image crashed for the 10<sup>th</sup> time I gave up! :)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>I have attached my test ogg file. You really want to
try it on a small file as it is SLOW :)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>Have fun<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-AU style='font-size:
10.0pt;font-family:Arial'>Russell<o:p></o:p></span></font></p>
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