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DAD hacking

Filed under: DAD — Thomas @ 00:06


On the bad side of life, I was planning to go to an awesome Calcotada in Lleida today, but I spent last night awake until 4:30 with an upset stomach, so I had to cancel and stay home feeling like shit.

On the good side of life, I really had no excuse left to not do a little long overdue hacking on Digital Audio Database.

I still use it regularly to listen to music, but the GNonLin-based player is just really not very stable. I should really just rewrite it using simply adder just like roughly ten years ago, but my brain won't be able to do that. So instead I decided to clean up the web-based WebSockets using player I prototyped at OVC last year.

I started with some refactoring, clearly defining model/view/controller base classes and adapting the player and playerview classes to them.

WebSocket code seems to need an update every few months - I pulled the latest revision of txWebsocket on my fork, so my recent browsers actually play music again.

Since the last time I hacked on this, I actually added my 1500+ freshly ripped cd's, in FLAC format - which browsers don't actually support.

So, first off, I added an option for the scheduler - responsible for picking tracks, and picking audio files to represent them - to filter by extension. It's not ideal, but it will do for now, and I punched that filter through the levels of abstraction in DAD. I now start it filtering on .mp3 and .oga, and so Chrome can play back all the tracks the scheduler throws at it.

The web-based player just loads tracks and timing info from the scheduler relative to page load time. I've been wanting to make that absolute for a while, so I did just that - the player server schedules tracks for epoch seconds now through websockets.

I had an entertaining half hour listening to the awesome echo effects obtained by having three chrome pages simultaneously playing the jukebox schedule - each page being slightly out of sync with the others.

As I'll be wanting to use a smallish computer for music playback using a browser, I adapted the code to not use localhost any longer, but do everything with relative URL's. Voila - the laptop now plays music too, a little bit more out of sync, and of course through its own speakers, adding to the eerie effect.

As an encore, I wanted to stumble my way through some jquery code, to which I'm a certified newbie. I want a nice background slideshow related to the current artist, and I pulled together echonest and bgstretcher-2 as an experiment.

That seems to work relatively well, except that the slideshow plugin doesn't let you reload a new set of images to cycle through. And some of the other ones I tried instead after that seemed to have the same problem.

Oh well, it's a start. If anyone knows of a good jquery background slideshow plugin that lets me update the list of url's for images at any time, let me know!

Adventures in fingerprinting

Filed under: DAD,Fedora,GStreamer — Thomas @ 20:55


One of the key concepts in my rewrite of DAD is that it should be possible to relate the same track across different files and computers. I have copies of files, and different encodings of the same track, spread across machines. Various applications I use for playback seem to exist in isolation on each machine, and so I tend to rate only occasionally knowing that my ratings aren't centralized. And I get annoyed when banshee detects three copies of an album, and then orders them by track number, playing each track three times before moving on to the next one.

The logical way to do is is through acoustic fingerprinting. These are algorithms that extract certain features from an audio file and calculate an algorithm-specific 'fingerprint' for it. Usually, these fingerprints are not identical across different encodings of the same file, so you can't look up twins in a list; but the fingerprints can be compared to each other and a 'difference' within a certain confidence interval calculated.

Most fingerprinting algorithms have a library that calculates a fingerprint and then submits it to a complimentary web service where it can quickly compare it to find twins.

In the past, either the client library/application or the web service (or both) was not open enough to be of interest for most Free Software people.

But recently, someone in the #morituri channel mentioned acoustid which only consists of open components. So, that seemed interesting enough to try out!

The chromaprint client-side library consists of a library, a sample application (linked against FFMPEG), and a python module with some sample scripts.

There is also a gst-chromaprint GStreamer plug-in on github. (As a side note, amazing to see that GStreamer plug-ins these days come for free! I recall the days when we had to the work ourselves to write GStreamer plug-ins for libraries)

So, after giving them a quick test run, I packaged up the whole set and it's now available for Fedora 14 and 15 in my package repositories

The chromaprint-tools package contains fpcalc and you need to enable rpmfusion-nonfree to get its ffmpeg dependency.

And after that, I created a Task in DAD for chromaprint, and now I have:

$ dad analyze chromaprint /opt/davedina/audio/albums/Afghan\ Whigs\ -\ Gentlemen/Afghan\ Whigs\ -\ Debonair.ogg
** Message: pygobject_register_sinkfunc is deprecated (GstObject)
/opt/davedina/audio/albums/Afghan Whigs - Gentlemen/Afghan Whigs - Debonair.ogg:
Found 1 results
- Found 4 recordings.
- musicbrainz id: 62b2952a-4605-4793-8b79-9f9745ea5da5
- artist: The Afghan Whigs
- title: Debonair
- musicbrainz id: 8ff78e73-f8bd-4d78-b562-c3e939fb93fb
- artist: The Afghan Whigs
- title: Debonair
- musicbrainz id: a0d5ced6-43e8-450a-bf11-94f1f4520b92
- artist: The Afghan Whigs
- title: Debonair
- musicbrainz id: d01ac720-874c-48d6-95c6-a2cb66f9d5d0
- artist: The Afghan Whigs
- title: Debonair


Now it's time to dump that in the couchdb database backend, and start identifying duplicate tracks.

Acoustid seems to be a relatively young project, but its maintainer is very active on the mailing list and it's filling a hole in the open world that I'm happy to see filled! Thank you Lukas.

Digital Audio Database

Filed under: DAD — Thomas @ 01:07


Over the past few years I've been quietly exploring ideas for my ideal music application. When I lived together in that great house in Gent, we had a hacky set of PHP code that let us import music, rate it, and have it play back. It worked for our purposes, but it was a collection of hacky PHP code and hacky Perl code.

Now I'm not saying I got that much better at coding, but I'm sure I improved a little bit. I've always put off actually writing the damn code to replace it, and hence I have a bunch of separate music collections - the music I was listening to in that house (properly rated, but very outdated), random collections of downloads, and now the collection of CD's I bought ever since leaving that house that never quite made it into my computer and are now being imported by the Lego robot.

Over a year ago, I re-implemented the mixing backend on top of GNonLin, which for the most part works as long as I don't actually dereference tracks played - somethign to figure out at some point. I have ideas about a pure web-based mixing backend as well, but I need to learn modern stuff like JQuery first.

But the missing key really was something that handles the database part well enough, because my application should work distributed - it should manage my tracks on all my devices, including all my computers, and be able to figure out that some crappy mp3 of a song on my laptop is the same song as the flac version at home on my NAS. So if I rate that crappy mp3 on my laptop, I want that taken into account when my home machine creates a mix.

And for me, CouchDB promised to fill that niche. Except of course that I spent the last year figuring out how I can marry CouchDB's approach to replication with my natural desire to denormalize. It turns out that's possible with CouchDB, but it involves doing a lot of client-side caching (and invalidating/changing on change notifications) and is already pretty slow when I do it for my 14000 test tracks.

So, I've decided to experiment in a world where normalization is not needed, and I'm just going to pick one central concept (The 'track'), store as much related data into that document as possible (on each computer, the fragments of audio files that represent that track; its ratings; what album it's on; which artists made the track), treat some of those values as caches for the last known value from parent documents, and just go for speed first and see how that goes.

Yes, I am going to relax about not having everything perfect on the inside, so I can move on and write some more code that I can actually use.

I enjoyed a lot trying to shoehorn CouchDB into my relational wordview, but I want to see what life is like on the other side.

Before I was also very focused on migrating my old data (from the music I had when I was in the house in Gent) and its ratings. That's still important to me, but I think right now I'd more enjoy having something that lets me listen to and rate new music. When I originally wrote DAD I didn't expect to be getting so much music that wasn't from CD's. That's obviously not the case anymore, and I'm probably one of the last maniacs still buying CD's and worrying about getting them sample-perfect onto my NAS. In today's reality I need to deal with having the same track fifteen times, in various qualities, and I wish my computer handled that for me.

As part of this shift in approach, both in how I use CouchDB and what music I now want to listen to, I'm going to build the code from the opposite side I've been doing, focusing on smaller building blocks and getting the experience right. Step one will be collecting the right data about audio files, splitting them into individual fragments, and loading music in two passes into the databases. I'll focus on having small tools that show that the application can add tracks quickly and start playing them, filling in the more costly information later, and show that the GUI frontend can update these in realtime in the database view.

And, as usual, I like to shoehorn in a use for my python command class, so I'll be using that as a collection point for these little tools as I work my way up.

After plugging in the right plumbing, in twenty minutes I had this on top of my old code:

$ dad analyze level /mnt/nas/media/davedina/audio/albums/Nirvana\ -\ In\ Utero/Nirvana\ -\ All\ Apologies.ogg
** Message: pygobject_register_sinkfunc is deprecated (GstObject)
Successfully analyzed file /mnt/nas/media/davedina/audio/albums/Nirvana - In Utero/Nirvana - All Apologies.ogg.
2 fragment(s)
- fragment 0: 0:00:00.000000000 - 0:03:50.230204081
- peak 0.240 dB (105.672 %)
- rms -14.199868248342282 dB
- peak rms -8.913940439528652 dB
- 95 percentile rms -12.001385041642244 dB
- weighted rms -14.202287606952533 dB
- weighted from 0:00:01.205986394 to 0:03:39.612879818
- fragment 1: 0:23:59.107482993 - 0:31:32.227482993
- peak 0.526 dB (112.876 %)
- rms -14.742109190444983 dB
- peak rms -8.729096757819718 dB
- 95 percentile rms -11.56951163744373 dB
- weighted rms -14.742603253857133 dB
- weighted from 0:23:59.223582765 to 0:31:18.498684807

In case you were wondering, this shows the code correctly determining that the 'All Apologies' track on the In Utero CD contains in fact two songs. It always annoys the hell out of me when any of the music players I use doesn't play anything for 20 minutes just because Kurdt thought that would be amusing all those years ago.

(In case you were really astute, you may have noticed that this code claims that the peak of these fragments is over unity, which would be weird and wrong you would think. Monty could give you a long and interesting explanation on how that is in fact natural and every time I read it I still don't get it, even with my audio engineering background, and I still don't know if this apparent peak level is a bad thing, but in practice my playback code auto-levels anyway and consistently reduces volume on tracks, so I don't think it matters anyway...)

Python 2.7, JSON, and unicode

Filed under: couchdb,DAD,General,Python,Twisted — Thomas @ 17:28


I have been hacking on Paisley more recently. I actually got to hack during work time on Paisley, because the guys needed a feature I had developed - change notification. But more on that later.

I eked out a four day hacking session over this easter weekend, and my primary goal is to make some good advances on my music database system using CouchDB. The code is still in prototype stage, and I wanted to start removing hacks, tightening things down, and adding tests. But suddenly I found myself having to add a bunch of unicode() calls on data coming back from paisley just because I was being stricter on the input to paisley functions.

I didn't want to have to deal with unicode, again, as it detracted me of the core of my application. But I didn't like paying the technical debt either of not understanding what was going wrong under the hood.

From my limited understanding, JSON is an object notation format used for exchange of information between processes and applications. A JSON string is in unicode, which is great. It would be pretty useless otherwise in today's world. So I should be able to send in unicode to JSON libraries and get unicode back out.

A recent change in Paisley by one of the maintainers prefers simplejson over the stdlib-json. I first thought this change was to blame for my problems.

And yes, when decoding a JSON object, text was returned as str instead of unicode objects. Now, this is only when the text is in fact ASCII and hence works fine both as str and as unicode. And I'm sure opinions will differ here - but I think that a JSON library should *always* deserialize text to the same type of object by default - ie, unicode.

Clearly, simplejson disagrees with me. But I didn't have this problem a few weeks ago, so something changed! What gives? And changing back to json over simplejson didn't fix it either!

After some googling, I stumbled upon this bug report. Apparently, in 2.7, the C-based implementation deserializes ASCII text as str instead of unicode. The Python-based one always returns unicode for text. And in previous Pythons, both always returned unicode for text.

In essence, my problem boiled down to this:

[thomas@ana ~]$ ipython
Python 2.7 (r27:82500, Sep 16 2010, 18:02:00)
Type "copyright", "credits" or "license" for more information.
IPython 0.10.2 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object'. ?object also works, ?? prints more.
In [1]: from json import decoder
In [2]: decoder.py_scanstring('"str"', 1)
Out[2]: (u'str', 5)
In [3]: decoder.c_scanstring('"str"', 1)
Out[3]: ('str', 5)


[py-2.6] [thomas@ana ~]$ python
Python 2.6.2 (r262:71600, Sep 29 2009, 21:49:07)
[GCC 4.4.1 20090725 (Red Hat 4.4.1-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from json import decoder
>>> decoder.py_scanstring('"str"', 1)
(u'str', 5)
>>> decoder.c_scanstring('"str"', 1)
(u'str', 5)

Note how the last command returned a normal str object.

And yes, in the past few weeks since I last tested this, I did indeed upgrade my machine to Fedora 14, pulling in Python 2.7

simplejson seems to always deserialize to str when it can. I would consider that a bug - ie, 'be strict in what you produce'.

As for Paisley, I made a feature-unicode branch on github, and this commit introduces a compatibility pjson module. By default it is STRICT, ie it wants unicode back always, and tests for the buggy behaviour, and does an alternative loads implementation that falls back to the python one. I'm sure some Paisley devs will prefer simplejson still, so you can change STRICTness and prefer simplejson.

Now, back to the hack.

Work weekend

Filed under: couchdb,DAD,GStreamer,Hacking,Music — Thomas @ 10:18


Since we are doing our yearly business planning weekend later this week, I had reserved the weekend to do work - mainly, put together eight (strike that, nine, our CEO added one at the 11th hour Sunday evening) presentations. But I wasn't getting into the groove of things, and procrastination hit.

So I wondered, what's the single most important thing that's been on my mind and that I'd do right now if I didn't have anybody else to answer to ?

And the answer was simple - I started another rewrite of DAD (Digital Audio Database) last year, this time based on CouchDB. I was in the middle of splitting up into a core (defining all base classes and simple implementations without any dependencies; for example, a pickle-based storage of the mixing data), a dadgst module (for a GStreamer-based player, since I will also have a pure web-based player), and a dadcouch module (for a CouchDB storage backend).

Before the split-up it was mostly a hardcoded GStreamer player playing from the pickle file, and a bunch of scripts to analyze files and put them into the pickle. I had not properly finished the CouchDB conversion - mostly, a bunch of methods that previously were synchronous now had to be made asynchronous with deferreds, and that was causing some conceptual issues (like, how to a lot of deferreds together - when chaining doesn't work, and parallellizing brings down your computer).

So, that's what I wanted to do this weekend first - get the couchdb backend to a state where it can select tracks slicing the audiofiles and providing the mixing information, and use the data from the old DAD database of now seven years ago. I want to hear those old songs again, according to my preference, and properly mixed. And with that in place, after a few hours of hacking, I could focus myself completely on the presentation preparing.

Well, completely except for the baby visits, the family lunching, and the pregnant friend visiting.

If you like looking at not-completely-finished-code that probably only I can get running usefully anyway, start here.

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