The Music Player Daemon, aka MPD, is a great little application to handle music on your linux computer. Until recently (when Linux really started to take off and gain popularity), MPD has been notoriously difficult to get to work properly. I decided to write this small intro to MPD after having used it for about 6 months. This is a little guide to it to get you started on using MPD as your music manager.

The World of MPD

First, what MPD is:

• MPD keeps track of your music library. It does this by defining a music directory, to which you can easily add symlinks to all the various places where you store your music on your computer.
• MPD tracks changes to your music library (any time an mp3 is removed, or a new album added, you simply update the MPD database file — which takes three or four seconds at most).
• MPD can store playlists.
• MPD can play songs, and output this information to various devices, such as your physical speakers (via alsa usually, but it can be any audio driver for your system), or even a http port for web access (via icecast).

What MPD is NOT (what most people get confused about):

• MPD cannot by itself determine: which songs are played and in what order. Nor does it come with any controls such as PAUSE, STOP, NEXT TRACK, etc. MPD, quite simply, can either: play a song, or do nothing while it is running. MPD’s behavior is controlled by clients, such as GMPC, Sonata, etc (my personal favorite is ncmpcpp).

The downside of this dichotomy between what MPD is and what it is not, is that you must install two applications to get the same functionality as any standard multimedia player like iTunes. However, there are many, many advantages of splitting up music-playing from music-controls. First, mpd will hardly crash and will be error-free due to its simple nature. Second, you gain the ability to access your large music collection from other computers in your home network without much fuss. This means that you could do things like: make your laptop act as a remote controller for your desktop’s speakers, or even create multiple MPD instances for specific purposes (e.g., alsa vs. icecast output).

Typical Setup

For most people, they only need one instance of MPD running — configured so that it plays songs directly to their computer speakers (with alsa output). So their MPD configuration file will look something like this (comment lines removed to save space):

music_directory "/home/shinobu/.mpd-untracked/music"
playlist_directory "/home/shinobu/.mpd-untracked/playlist"
db_file "/home/shinobu/.mpd-untracked/mpd.db"
log_file "/home/shinobu/.mpd-untracked/mpd.log"
error_file "/home/shinobu/.mpd-untracked/mpd.error"
pid_file "/home/shinobu/.mpd-untracked/mpd.pid"
state_file "/home/shinobu/.mpd-untracked/mpdstate"
user "shinobu"
bind_to_address        "localhost" # if no one else on the LAN wants to use this mpd; otherwise use local IP address
port                "6600"
audio_output {
    type            "alsa"
    name            "Exelion ALSA output"
}
mixer_type            "alsa"
mixer_device            "default"
mixer_control            "PCM"
replaygain            "track"
filesystem_charset        "UTF-8"
id3v1_encoding            "ISO-8859-1"

It’s very straightforward. All of the essential files and folders are customized and defined in the config file. (My mpd directory is .mpd-untracked, since these files/folders are not tracked by my git folder containing all of my dotfiles. See my previous two posts for more info on that setup.) The config file itself resides at /home/shinobu/sycfg/mpd/cfg-alsa — a customized path and filename, which is referenced each time MPD starts on bootup (in my .xinitrc file), with the command “mpd /home/shinobu/syscfg/mpd/cfg-alsa”. MPD will daemonize itself when it is called, so calling it from your .xinitrc file without the “&” argument at the end of the line is OK. Notice how the above configuration avoids running into permission problems, since everything resides under a normal user’s directory.

I then start up ncmpcpp, which by default looks to the mpd host as localhost and port as 6600 — matching the (default) values in my MPD config file above. And it all works rather beautifully.

Multi-MPD Setup for Music Sharing

Back when I still used iTunes (about 3 years ago), I remember it had this neat feature to share your music with anyone on your local network. You can do the same thing with MPD. The trick is to add a separate MPD instance for this very same feature. I myself have this multi-MPD setup on my desktop, with one MPD for alsa-only output (as seen above), and a second MPD for icecast-only output. Icecast, by the way, is a more general solution not wholly related to MPD for sharing music over the internet — we can use icecast since it plays rather well with MPD. Since my desktop has a second MPD instance so that it works with icecast, my laptop can now take advantage of the huge music collection that I have on it, remotely (well, as long as I’m on the home network in my case).

Here’s my MPD config file for icecast output:

music_directory "/home/shinobu/.mpd-untracked/music"
playlist_directory "/home/shinobu/.mpd-untracked/playlist"
db_file "/home/shinobu/.mpd-untracked/mpd.db"
log_file "/home/shinobu/.mpd-untracked/mpd-icecast.log"
error_file "/home/shinobu/.mpd-untracked/mpd-icecast.error"
pid_file "/home/shinobu/.mpd-untracked/mpd-icecast.pid"
state_file "/home/shinobu/.mpd-untracked/mpdstate-icecast"
user "shinobu"
bind_to_address		"192.168.0.7" # bind it to this computer's IP address if someone on the LAN wants to use this mpd
port				"6601"
audio_output {
    type			"shout"
    name			"exelion HD mpd stream"
    encoding		"ogg"			# optional
    host			"localhost"
    port			"8000"
    mount			"/mpd.ogg"
#--------------------------------------------------------------------------------------------------#
# See 'source password' in /etc/icecast.xml for password                                           #
#--------------------------------------------------------------------------------------------------#
    password		"hackme"
#--------------------------------------------------------------------------------------------------#
# Use 'bitrate' or 'quality'. Use 'bitrate' for static bitrate, or 'quality' for variable.         #
# Use one or the other -- not both!                                                                #
# bitrate                     "128"                                                                #
#--------------------------------------------------------------------------------------------------#
    quality			"10"
#--------------------------------------------------------------------------------------------------#
# 'format' is the audio format of the stream. The first number is the sample rate in Hertz (Hz);   #
# 44100 Hz is equal to cd quality. The second number is the number of bits per sample; again 16    #
# bits is the quality used on cd's. The third number is the number of channels; 1 channel is       #
# mono, 2 channels is stereo.                                                                      #
#--------------------------------------------------------------------------------------------------#
    format			"44100:16:2"
    protocol		"icecast2"		# optional
    user			"source"		# optional
    #description		"My Stream Description"	# optional
    #genre			"jazz"			# optional
    #public			"no"			# optional
    #timeout			"2"			# optional
}
mixer_type			"alsa"
mixer_device			"default"
mixer_control			"PCM"
replaygain			"track"
filesystem_charset		"UTF-8"
id3v1_encoding			"ISO-8859-1"

As you can see, much of the configuration is exactly the same as my first MPD config file. You’d want it like this, since you’d want it to use the same music collection and list of playlists. So the music directory, playlist directory, and database file are all the same. However, you’d want a different set of logfiles for this second MPD instance, so those values are changed. The same goes to the pid and state files.  The other noticeable differences are the bind_to_address value, set to my desktop’s IP address. The port number is also 6601, so that it doesn’t conflict with my first MPD. The final difference is the audio output, which is set to “shout” and not “alsa”. The “shout” output works with icecast, and the values in here, like port 8000 and “hackme” as the password, are taken straight from the default icecast intallation’s xml file (/etc/icecast.xml — of course, you can call icecast with a different config file location than the default one).

It’s important that you make this second MPD output solely to icecast. If you put in alsa output here, you’d have two different songs playing simultaneously on your desktop’s speakers! (Aside: MPD is perfectly capable of outputting to multiple audio outputs, so you could, if you wanted, make one MPD instance output to both alsa and icecast — although I don’t see why anyone would do this.) As for icecast itself, you can also call it from your .xinitrc file, after your mpd-calling lines, like so: icecast -b -c /home/shinobu/syscfg/icecast/cfg.xml. The -b flag daemonizes icecast (required since you’re calling it from your .xinitrc file), and the -c flag merely points to the correct config file location. My icecast config file looks like this:

<icecast>
    <limits>
        <clients>100</clients>
        <sources>2</sources>
        <threadpool>5</threadpool>
        <queue-size>524288</queue-size>
        <client-timeout>30</client-timeout>
        <header-timeout>15</header-timeout>
        <source-timeout>10</source-timeout>
        <burst-on-connect>1</burst-on-connect>
        <burst-size>65535</burst-size>
    </limits>
    <authentication>
        <source-password>hackme</source-password>
        <relay-password>hackme</relay-password>
        <admin-user>admin</admin-user>
        <admin-password>hackme</admin-password>
    </authentication>
    <hostname>localhost</hostname>
    <listen-socket>
        <port>8000</port>
    </listen-socket>
    <fileserve>1</fileserve>
    <paths>
        <basedir>/usr/share/icecast</basedir>
        <logdir>/home/shinobu/.icecast-untracked/log</logdir>
        <webroot>/home/shinobu/.icecast-untracked/icecast/web</webroot>
        <adminroot>/home/shinobu/.icecast-untracked/icecast/admin</adminroot>
        <alias source="/" dest="/status.xsl"/>
    </paths>
    <logging>
        <accesslog>access.log</accesslog>
        <errorlog>error.log</errorlog>
        <loglevel>1</loglevel> <!-- 4 Debug, 3 Info, 2 Warn, 1 Error -->
        <logsize>10000</logsize> <!-- Max size of a logfile -->
    </logging>
    <security>
        <chroot>0</chroot>
    </security>
</icecast

Here, the value for the <source-password> tag must match the password specified in your icecast-MPD’s config file. I’ve left it to the default “hackme” here for demnstration purposes — you should change it to something more secure (better safe than sorry!). My password is like @#$k23lsdf9. Make sure the directory in <logdir> exists. As for the <webroot> and <adminroot> directories, copy them straight out of /usr/share/icecast/web and /usr/share/icecast/admin, and place them into your custom location. This will take care of those annoying permission errors that users often face.

Now, on your remote computer, such as your laptop, you need (1) an MPD client, and (2) a music player, like mplayer, to intercept the raw .ogg music stream from your desktop with the icecast-MPD setup. In my ncmpcpp config file on my laptop, I have custom values for the mpd_host and mpd_port fields to be my desktop’s IP address 192.168.0.7 and 6601, respectively (matching the values in the second MPD config file above). So when I fire up ncmpcpp on my laptop, it connects over the LAN network into the music collection residing in my desktop, all with the magic of MPD. Once I activate the ogg stream by playing a file, I can then access this stream with mplayer — specifically, with mplayer -ao alsa -softvol -volume 10 -volstep 1 -prefer-ipv4 http://192.168.0.110:8000/mpd.ogg. I have this long command aliased, of course, to a hotkey in my XMonad configuration file. And within a couple seconds, I get a top-quality, ~500 kbps ogg stream right on my laptop (the quality setting in my MPD config file, set to “10″, is the maximum quality supported by the ogg format; 500 kbps, or a little over 60 KBps, should be nothing on your home ethernet LAN).

So here’s what’s happening with this second MPD instance on my desktop, configured with icecast output: MPD is keeps tabs on what my music collection consists of from port 6601, and “plays” to port 8000 — converting my current mp3/flac file into an ogg stream, which is then served by icecast. From my laptop, I then connect to this MPD by the desktop’s IP address and MPD port of 6601 with ncmpcpp. Then, once I tell MPD to start playing, I can then access the ogg stream with mplayer on my laptop. Mplayer simply looks to http://192.168.0.7:8000/mpd.ogg. When icecast on my desktop receives this request from my laptop’s mplayer, it gives the go-ahead and essentially acts as a bridge between my desktop’s icecast-output MPD and my laptop’s mplayer. Mplayer then takes this ogg stream, and outputs it onto my laptop’s speakers using the alsa drivers.

Here’s a picture to describe what’s going on. (The latest OpenOffice.org Drawing app is really a pleasure to use!)

So I hope this post proves useful to people who are new to Linux and are struggling to get MPD (and especially with Icecast) to work.

I’ve done a few things here and there this winter break. My law school career is coming to an end — I’ve just 1 more semester to go! Anyway, you can tell from this blog’s evolution that that I like to blog mostly about techie/geeky/nerd things like computer programming, linux, and the like. So that’s what I’ve been doing these days — my most precious, last real “winter break” before getting a job in the real world. Yes, I could work for someone — but I’m going to be working the rest of my life!

Some things I’ve done recently, or am getting into:

• I got rid of Xubuntu (gasp!) on my old laptop, and replaced it with Arch Linux, after hearing one rave review of it after another. This is the distro that has slowly and steadily climed up in popularity on DistroWatch, enough to rival and surpass Gentoo, while being similarly focused on simplicity and end-user configuration (not “factory defaults” like Ubuntu or Mint). The install and setup wasn’t so smooth, as the wikis and beginner guides were, though highly informative, not really comprehensive. But after I got it running — I too have been generally impressed with Arch, and the whole Arch community, and its pacman packaging system, along with the ABS/AUR duality for getting packages.
• I started learning text-based (aka “console” or CLI for command line interface) clients for many common things I do on the computer. So far I’ve managed to use and configure irssi for IRC, and I also use aria2 for bittorrent. I want to look into tmux (replacement for GNU Screen), alpine (email client), bitlbee (for AIM, MSN messaging from inside irssi), and clex (file manager). Why a sudden emphasis on console clients, instead of graphical ones based on GTK or KDE? Well, for one, text-based ones run faster, and are more stable. And once you set up text-based clients and have them configured properly, they are easier to use and are much more efficient time-wise to get the same thing done.
• I switched my default shell from bash to zsh. The tab-completion feature alone makes the switch worth it, in my opinion, as well as the somewhat-difficult-but-doable themeing of the prompt. There are tons and tons of features in zsh that are customizable (the man page for zsh is broken up into 17 sections!), that I will slowly start to learn as I get more and more into programming as a hobby (shell programming, to be more exact).
• I stopped using xfce4-terminal (aka “Terminal” in the XFCE desktop environment) because of its poor color support (it only has 16? colors) and, after a series of changes, finally settled on a custom, AUR-based package of urxvt (rxvt-unicode) that supports 256 colors. Now my vim looks virtually the same as my gvim using the zenburn theme. Yay!
• I started exploring other programming languages a little bit. So far, I’ve decided to get more into Haskell and Factor. Haskell has a reputation for being rock solid, from what I can glean from the blogs and news sites out there, while Factor is cute and interesting with its stack programming model. I also want to ditch Ruby and get into Python (I’m tired of writing “end” over and over again), so I’ll look into that more in the future (although, this would mean that I would have to rewrite my custom Rails app that I made last year using Django or something else, even — but I think the sacrifice would be worth it).
• I got back into practicing the guitar again — but this time focusing only on my classical guitar and playing older songs (not modern ones from rock bands) like the short pieces by Carcassi.

I’ll probably write the obligatory Arch Linux “first impressions” review in the future, from my unique experience of having switched from Linux Mint to Xubuntu to Arch Linux in the course of about 1 year, never having used Linux in the past. Was the switch to Arch worth it? Yes. I’ll explain as much as I can, and why you should also switch, in the review.

So today I went to Ono’s with my roommate again in Westwood. We had actually planned to go to the sushi place by Rite Aid, but that place was closed since it was Sunday. Unfortunately Ono’s didn’t live up to the reputation of its glory days of yore, and we felt very disappointed after ordering our usual BBQ Mix #4 (rice, macaroni salad, 갈비 ribs, chicken, and beef).

But at least I went to a Korean bar/restaurant yesterday in K-town with my good friend Jake (a.k.a. Yoon-san). I had some beer and chicken (hot wings)… it was really excellent. We talked a lot about girls, religion, and people in general and it was very fun. Hopefully I’ll get to go to a 노래방 (Karaoke bar) in the future with him and some other people…

And for those who are interested I am watching an anime called Honey & Clover in my free time. It’s very funny, and a bit reminiscent of the style in Azumanga Daioh, but toned down a bit. The rhythm of the plot of each episode is so well paced that I don’t even notice the passage of time as much as I do in other anime.

Peace.

So today I spent my evening with a couple of Japanese friends, and we ended up going to a Japanese bar. It was interesting, and although I only had 2 beers, it was still very fun and exciting. I'll definitely go again, given a chance.

I was talking to my new friend Junpei, and somehow my going to law school this fall came up during the conversation. Apparently, I look very mature as a person and highly motivated to go to law school. Hooray.