MPRIS2 and the Music Player Daemon

If you tend to want to keep your music running when you log out, or control your music playing on a desktop machine from a laptop, for example, you may well use the Music Player Daemon (MPD).  If you use Ubuntu’s Unity desktop or KDE’s Plasma desktop, you may well wonder how to get the Ubuntu sound menu or Plasma’s Now Playing widget to talk to it.

Both of these use MPRIS2 to communicate with media players.  MPD, however, does not have an MPRIS2 interface.  Even if it did, it would take a bit of work to be able to use it from another computer.  What you need, then, is a “bridge” of some sort to translate.  One such possibility is mpDris2 (which, I hasten to point out, I haven’t tested).

You would run such a bridge on the computer you want to control MPD from, and point it to your MPD instance.  And voilà!  Every MPRIS2 client application that you run can talk to MPD, without knowing anything about the MPD protocol.

If you just want a headless music player on your local machine, though, you can always use Raven, which talks MPRIS2 natively.

New Now Playing Plasmoid, MPRIS2 dataengine

One thing that will be in KDE Plasma Desktop 4.9 is a new version of the Now Playing widget.  Based on QML, it works much better, especially on panels (where its design is based heavily on my favourite KDE-3-era applet, kirocker).

Now Playing on a panel

In the background, it uses the new mpris2 dataengine.  This exclusively supports MPRIS2-capable media players (which these days is most), and doesn’t include any hacks to support XMMS 1, for example.  JuK and Dragon have both gained MPRIS2 support for the 4.9 release, and Ubuntu’s sound menu uses MPRIS2, which is compelling many other media players to support it.

Now Playing on the desktop

The result is a cleaner, more reliable design, and completely asynchronous behaviour, so it will use less power and (unlike the old nowplaying dataengine) it should never cause your desktop to freeze due to a badly-behaving media player.

Now Playing with the mouse over

The old nowplaying dataengine is still there (and will be until KDE Plasma Desktop 5 is released), but should not be used for new widgets.  Instead, you should use the mpris2 dataengine, and I highly recommend porting any existing widgets to mpris2 as well.

Overall, I’m really pleased with the design of MPRIS2, which allowed me to create the mpris2 dataengine with a minimum of fuss, and allowed for widgets to implement a seek bar without querying the media player once or twice a second to find the current position (and not take the performance/power hit if they didn’t care about the current playback position).

MPRIS2 Support in NowPlaying

Do you recall NowPlaying?  The dataengine/widget pair for Plasma that tells you what your media player is currently playing, and allows you to control it?

The Now Playing widget (with an old theme)

Well, now it supports MPRIS2.  What does this mean for you?

Well, probably not much right now.  Juk doesn’t support MPRIS2 (although I intend to change that for 4.9/5.0), Amarok worked before (although it should use marginally less power with MPRIS2 rather than the old MPRIS interface), VLC doesn’t support MPRIS2 (yet; version 1.2 will).  A handful of other players support MPRIS2, though, including the Raven Music Server.

The main thing, though, is that support for MPRIS2 is increasing in media players, partly because of Ubuntu’s adoption of it as the mechanism for its sound menu to talk to media players.  Spotify now supports MPRIS2, for example.  And now the Now Playing widget can support them.

MPRIS2 has many advantages over the original MPRIS specification, not least of which is not having to query the media player every second for up-to-date position information.  As a result, the nowplaying dataengine will prefer the MPRIS2 interface to the MPRIS interface for a media player that offers both.

The only quirk to be aware of is that Amarok’s MPRIS2 support isn’t quite right in the 2.4.x series, and this will affect a couple of features of the Now Playing widget (seeking and enabling/disabling of the next/previous buttons); this shouldn’t be an issue though, as these problems are fixed for Amarok 2.5, which will be released before KDE Plasma Workspace 4.8.

Guademy

It’s been a while since I posted. Such is life.

I’m really enjoying my first Akademy. I managed to forget a power adapter to convert between my British plug and the European sockets, but Nuno lent me one for a few days. I now have to find my own, though, as he went home today.

So, the conference. The keynotes on Saturday morning were really good. I recommend watching them when the videos are online (which they may be already). Of course, there is some furore over Richard Stallman’s talk, but I think that was always expected.

Yesterday was the KDE e.v. meeting, which I didn’t go to (not being a member of the e.v.). Instead, I slept in (sleep has been in short supply), went to the beach, and hacked. I put together a small plasmoid (87 lines of javascript) to show some controls for a media player. The idea is that you can put this on an auto-hiding panel on your desktop so that they don’t take up screen real estate, but are easily accessibly just by moving your mouse. The other half of the job, of course, is to do one that displays information. Then you can have the information about what song is currently playing permanently visible, and the controls only appear when you want them.

Today we had a very productive discussion on moving KDE to Git. The aim (if everything goes swimmingly) seems to be to move before KDE 4.4 goes into freeze. Amarok is intending to move very soon, though.

Speaking of Amarok, we’ve been sitting in one of the labs discussing things since the Git BoF. It’s amazing how much gets decided how quickly, especially when you’re used to deciding things on mailing lists. This is particularly true for user interface decisions. I’m expecting great things from the next release of Amarok.

What’s Playing, Doc?

So, I was round at a friend’s, and he was playing with Amarok and the Plasma widgets screensaver, and wanted a way to see what was currently playing when his computer was locked.  Of course, I pointed him towards the Now Playing applet, but it was overkill for what he wanted – he didn’t want the buttons, or the sliders – just a display of the current information.  Well, I was in the mood for playing, and it took me about 15 minutes to construct a javascript plasmoid, most of which was spent researching how to use data engines from them.

The code I left him with was:

layout = new LinearLayout(plasmoid);
layout.setOrientation(QtVertical);

label = new Label();
layout.addItem(label);
label.text = 'No player'

plasmoid.dataUpdate = function(name, data) {
    label.text = 'Info:\n';
    for (var key in data) {
        label.text += key + ': ' + data[key] + '\n';
    }
}

plasmoid.dataEngine("nowplaying").connectSource("org.mpris.amarok", plasmoid, 500);

This was in a file called “main.js” in a subfolder called “contents”. In the plasmoid folder (the folder containing the contents folder), I also put in a metadata.desktop file:

[Desktop Entry]
Name=Simple Now Playing
Comment=Now Playing as Matt likes it
Icon=applications-multimedia
Type=Service
X-Plasma-API=javascript
X-Plasma-MainScript=main.js
X-Plasma-DefaultSize=200,100
X-KDE-ServiceTypes=Plasma/Applet
X-KDE-PluginInfo-Author=Alex Merry
X-KDE-PluginInfo-Email=alex.merry [SPAMNO]@[SPAMNO] kdemail.org
X-KDE-PluginInfo-Name=simplenowplaying
X-KDE-PluginInfo-Version=0.1
X-KDE-PluginInfo-Website=http://plasma.kde.org/
X-KDE-PluginInfo-Category=Multimedia
X-KDE-PluginInfo-Depends=
X-KDE-PluginInfo-License=GPL
X-KDE-PluginInfo-EnabledByDefault=true

Now it was just a case of calling plasmapkg -i . from within the plasmoid directory, and the simple widget was installed. This produces the following:

Of course, this will only work with Amarok, and doesn’t respond to Amarok being started or quit. That’s OK, it’s not much more work to deal with that:

layout = new LinearLayout(plasmoid);
layout.setOrientation(QtVertical);

label = new Label();
layout.addItem(label);
label.text = "No player found";

function firstSource() {
	var sources = plasmoid.dataEngine("nowplaying").sources;
	if (sources.length) {
		return sources[0];
	} else {
		label.text = "No player found";
		return '';
	}
}

plasmoid.dataUpdate = function(name, data) {
	if (source == name) {
		label.text = 'Info:\n';
		for (var key in data) {
			label.text += key + ': ' + data[key] + '\n';	
		}
	}
}

source = firstSource();

npDataEngine = plasmoid.dataEngine("nowplaying");

npDataEngine.sourceRemoved.connect(function(name) {
	if (name == source) {
		source = firstSource();
		if (source) {
			npDataEngine.connect(source, plasmoid, 500);
		}
	}
});

npDataEngine.sourceAdded.connect(function(name) {
	if (!source) {
		source = name;
		npDataEngine.connect(source, plasmoid, 500);
	}
});

if (source) {
	npDataEngine.connectSource(source, plasmoid, 500);
}

Of course, it’s not much work to only show the things you’re interested in, but this covers the interesting parts of the plasmoid.

Interesting note: it appears that if you replace the line label.text = 'Info:\n'; with label.text = '';, the subsequent calls to label.text += ... don’t work – you just end up with a blank label.

Resizing plasmoids

Until this morning, resizing plasma applets meant maintaining the aspect ratio. There was no way to make them wider without changing the height, or vice versa, without manually editing the plasma config file.

Well, if you are running trunk, you can now freely resize applets by holding CTRL while resizing. This won’t make it to 4.0.0 (which has already been tagged), but all the current fixes in plasma should be backported to the 4.0 branch before we move on to 4.1 development. So it should make it to 4.0.1, which is good as it’s quite an important feature for certain plasmoids.

Also, I’ve greatly improved the Now Playing applet:

The text size will stretch to fit the height of the applet and, if the text doesn’t fit the width of the applet, any excess text will be ellided:

This is why I needed free resizing…

Now Playing: MPRIS

MPRIS is insane. MPRIS is well-thought out. MPRIS is a standard for querying and controlling any media player without having to know the details of each player’s remote interface. MPRIS is now supported by the Now Playing data engine.

All of the above statements are true, to varying degrees.

It’s insane because it uses the same interface name (org.freedesktop.MediaPlayer) for three different interfaces (one for each of the objects /, /Player and /TrackList). This causes havoc with Qt’s D-Bus interface compiler. Luckily, just about everything I need is exported by the /Player part of the interface. Unfortunately, the only way to get the current track number out of Audacious is using the /TrackList object.

It’s well-thought out in most other respects. It has signals for information changes (something missing in Juk’s D-Bus interface). It is generally adaptable to the capabilities of most media players, without going overboard. It has a sane system of informing clients about the capabilities of the player’s interface (such as whether you can skip to the next track, for example), even if Audacious isn’t entirely honest about what is possible.

It’s a universal standard that allows clients to be player-agnostic. Or, at least, that’s the idea. Currently, I can only find one client supporting it: Audacious (although VLC 0.9.0 should include MPRIS support). And Audacious diverges from the standard in a couple of respects, most noticeably in the metadata returned for a track. It doesn’t include the tracknumber (which is optional, but it would be nice if it returned it when it made sense). It uses “length” for the length of the track in seconds, rather than “time”. And, outside the metadata, it claims every action is possible, even when it isn’t, such as stopping when nothing is playing.

The Now Playing applet support MPRIS players. Or, at least, it supports Audacious, which is the only one I’ve tested it with. And it doesn’t give a track number even then. But hey, it’s better than nothing, right? And other players should work “out of the box”, providing they don’t need any hacks like Audacious’ length/time metadata issue.

So: Juk and MPRIS players are supported. Next, I think I’ll steal XMMS support from the Kopete Now Listening plugin.

Incidentally, the player-querying code in the Now Playing engine should be general enough to use with other projects that need to get this information. One possible future change is to make them plugins that can be loaded by anyone who wants them.

PS: Is it me, or are there loads of media players that all seem exactly the same (WinAMP, Audacious, XMMS, Beep)?