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LPD For Fun and MP3 Playing
poop writes "Most true Unix geeks will recognize just how nice LPD is as a distributed queueing mechanism for managing all jobs sent to the printer. But, what most people don't realize is that LPD can be used for other things too. In fact, it can be viewed as a general queueing mechanism with a few added bells and whistles for printers. So let's examine a more interesting use of LPD, an engine for distributed spooling of MP3s." Bruha points out this mirror.
this has been getting a lot of coverage this week (article on deadly, some canadian newspaper, and now here). they did it at the obsd hackathon last year, and again this year.
lpd is quite cool. i've used it to queue software builds on remote machines where we aren't given ssh accounts. it's pretty slick.
vodka, straight up, thank you!
I don't normally do this, but as the site seems to be almost dead within the first three posts, I've duplicated the article content in this post.
/etc/printcap on my redhat 7.3 system (no sound card on the openBSD firewall) it is /etc/printcap.local. You'll want to paste the following snipped of code in there:
:lp=/dev/null:\ :sd=/var/spool/lpd/audio:\ :if=/usr/local/bin/audiofilter:\ :af=/var/log/audio-acct:\ :lf=/var/log/audio-errs:\ :sh
:lp=/dev/null: - we're not hooking this up to a physical device in the normal sense :if=/usr/local/bin/audiofilter: - this is the input filter. I'll show how to create it later. :af=/var/log/audio-acct: - this is the accounting file. You could do some fun stuff with this to monitor who uses the queue the most and what not. :lf=/var/log/audio-errs: - this is the file that errors will be logged to. Well, some errors; not all errors will end up here. :sh - tells it to supress any header information that would normally be sent. This is important or you may get junk before every file which causes audiofilter to fail.
/usr/local/bin/audiofilter:
;; ;; ;;
-- article --
May 23, 2003
LPD for fun and MP3 playing
Background
Most true Unix geeks will recognize just how nice LPD is as a distributed queueing mechanism for managing all jobs sent to the printer. It has a beautiful simplicity to it, and some mean power to go along with it. It's a difficult beast to tame, but once you understand it, everything will start coming out exactly like you want it.
But, what most people don't realize is that LPD can be used for other things too. In fact, it can be viewed as a general queueing mechanism with a few added bells and whistles for printers. So let's examine a more interesting use of LPD, an engine for distributed spooling of MP3s.
Motivation
The main thing that got me started on this quest was seeing these two pictures (one, two) from the c2k3 openBSD hackathon I saw that obviously someone else had figured out how to do it. I sure as heck could also.
Initial Assessment
The first stop on my quest was examine the all-knowing seer of the Internet, google. That returned a wonderful page in Swedish about how to do this very task. Unfortunately, my swedish sucks, but thankfully the scripts were written in bash, and the other big thing was just a printcap file.
Creating a Printcap Entry
The first thing that you need to do is to create an entry in your printcap file for your shiny new mp3 printer. On most systems this file is
mp3:\
Now we'll walk through the entry line by line. I'll ignore the \ at the end of almost every line, that just tells lpd to keep reading because there is more to come. The last line doesn't need the \ obviously.
* 1: mp3: - the name of your mp3 printer. In this case, just mp3
* 2:
* 3:
* 4:
* 5:
* 6:
An Audio Input Filter
The key to the whole system is that all of the processing is done by input filter. On some platforms this may cause it say that the printing has stalled while a song is playing, but that's not a big deal. There is no output from the input filter, and thus nothing is done after this. You'll want to put the following piece of code on your system as
#!/bin/bash
#
# This script was originally made by Teddy Hogeborn.
# Small alterations was made by:
# Peter Lundqvist
# Patrick Wagstrom
#
# This is a "printer filter" for playing audio files
for arg in "$@"; do
case "$arg" in
-d*) dir="${arg#-d}"
-e*) basefile="${arg#-e}"
-f*.*) ext="${arg##*.}"
esac
done
mp3player="mpg123 -q -o oss";
modplayer="mikmod --quiet --playmode 0 --noloops --
And enjoy. Don't mod me up though, it would be karma-whoring.
And wanted to add that the idea isn't new as you can see in this recent thread on deadly.org here (See post "mp3's playing via lpr?").
I like CUPS's mechanism for this kind of thing even more. You basically have two components, a filter and a backend. The filter takes in one a few forms of input (mostly postscript, but plain text and some image formats also) and dumps out the native data format of the selected printer model (or just echos the input if you set it as a raw queue). The backend is then responsible for somehow getting it to the printer, either queueing it on the parallel port or sending it out on the network somehow, or anything else.
Some fun things I've done with backends:
Network printing over SSH
Text-to-speech queueing (print your source code to hear it read aloud by festival)
Dumping into a jpeg as a way of snapshotting any document you might want to save
Dumping into a PDF with ps2pdf to make your Windows friends feel stupid for buying Distiller =)
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There are already some emacs mp3 players.
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