Speeding through the crisis (22 Apr 2009)

That darn ol' MP3 player. Five years old, but still looks cute. Stubbornly refuses to break, too, so no excuse to go out and buy a new one. Which, of course, I wouldn't do anyway these days. You know, the crisis and all - who has the guts to make investments like this now. I mean, a new player could easily cost me as much as 30 euros! wink

So I'm sticking to the old hardware, and it works great, except for one thing: It cannot set bookmarks. Sure, it remembers which file I was playing most recently, but it doesn't know where I was within that file. Without bookmarks, resuming to listen to that podcast of 40 minutes length which I started into the other day is an awkward, painstakingly slow and daunting task.

But then, those years at university studying computer science needed to finally amortize themselves anyway, and so I set out to look for a software solution!

The idea was to preprocess podcasts as follows:

  • Split podcasts into five-minute chunks. This way, I can easily resume from where I left off without a lot of hassle.
  • While I'm at it, speed up the podcast by 15%. Most podcasts have more than enough verbal fluff and uhms and pauses in them, so listening to them in their original speed is, in fact, a waste of time. Of course, I don't want all my podcasts to sound like Mickey Mouse cartoons, of course, so I need to preserve the original pitch.
  • Most of the time, I listen to technical podcasts over el-cheapo headphones in noisy environments like commuter trains, so I don't need no steenkin' 320kbps bitrates, thank you very much.
  • And the whole thing needs to run from the command line so that I can process podcasts in batches.

I found it surprisingly difficult to find the single right tool for the purpose, so after experimenting for a while, I wrote the following bash script which does the job.

#! /bin/bash
# Hacked by Claus Brod, 
#   http://www.clausbrod.de/Blog/DefinePrivatePublic20090422SpeedingThroughTheCrisis
# prepare podcast for mp3 player:
#  - speed up by 15%
#  - split into small chunks of 5 minutes each
#  - recode in low bitrate
# requires:
#  - lame
#  - soundstretch
#  - mp3splt

if [ $# -ne 1 ]
  echo Usage: $0 mp3file >&2
  exit 2

bn=`basename "$1"`

lame --priority 0 -S --decode "$1" - | \ 
  soundstretch stdin stdout -tempo=15 | \ 
  lame --priority 0 -S --vbr-new -V 9 - temp.mp3

mp3splt -q -f -t 05.00 -o "${bn}_@n" temp.mp3
rm temp.mp3

The script uses lame, soundstretch and mp3splt for the job, so you'll have to download and install those packages first. On Windows, lame.exe, soundstretch.exe and mp3splt.exe also need to be accessible through PATH.

The script is, of course, absurdly lame with all its hardcoded filenames and parameters and all, and it works for MP3 files only - but it does the job for me, and hopefully it's useful to someone out there as well. Enjoy!

Reasons To Admire Lisp (part 1) (16 Apr 2009)


When I tell people that I like and admire Lisp, they will typically roll their eyes and/or give me some pretty weird looks - and then they'll ignore me for the rest of their lives.

Well, after all those years, I'm usually not hurt anymore. Instead, I just giggle to myself like the proverbial mad scientist. You see, in the past few years there has been such a huge surge of interest in functional and dynamic languages that everybody and their sister already programs in a Lisp-like language, only without knowing it. Or, at the very least, they use a language or programming environment whose designers adopted very significant amounts of Lispy concepts. Examples: C#, JavaScript, Ruby, Python, Scheme, Groovy, Perl, Smalltalk, Java - and, in fact, pretty much any language running on top of the CLR or JVM. (Heck, even C++ programmers will soon learn lambdas and closures...)

Being an old fart, my memory doesn't serve me as well as it used to, hence my bias towards simple concepts and simple solutions which are easy to memorize.

For starters, a compelling reason to fall in love with Lisp is its syntactical simplicity. Lisp probably has the easiest syntax of all programming languages, maybe with the exception of Forth-like languages. Want proof? This morning, a good soul over at reddit pointed me to results of the University of Geneva's HyperGOS project: A comparison of BNF graphs for various languages. Lisp's BNF looks like this:

s_expression = atomic_symbol / "(" s_expression "."s_expression ")" / list 

list = "(" s_expression < s_expression > ")"

atomic_symbol = letter atom_part

atom_part = empty / letter atom_part / number atom_part

letter = "a" / "b" / " ..." / "z"

number = "1" / "2" / " ..." / "9"

empty = " "

Now compare the above to, say, Java. (And yes, the description above doesn't tell the whole story since it doesn't cover any kind of semantic aspects. So sue me.)

Oh, and while we're at it: Lisp Syntax Doesn't Suck, says Brian Carper, and who am I to disagree.

So there.

Previous month: Click here.

Revision: r1.4 - 30 May 2009 - 22:08 - ClausBrod
Blog > DefinePrivatePublic200904
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