I just fixed four major blockers in ZX2C4 Music. I also moved the source into a public git.

Prior to the fix, only one php page could load at a time. When requesting a second php page while one was loading, the request would hang until the previous one had completed. This is not terribly problematic for ordinary web pages, but because I use php for file downloads, the entire web app would hang until the file had completed downloading. Bad news bears. After a lot of difficult debugging, tcpdumps, header inspects, ps aux, etc, I discovered the problem to be with session_start(). It turns out that only one session can be opened for writing at a time per session cookie, which means for a single user, php will only allow pages to write to his session one at a time. The solution was to call session_write_close() immediately after editing the last $_SESSION variable.

Some media players had trouble seeking in streams from the php file streamer because of bad http header range support. The sendFile() is now HTTP/1.1 compliant. Although, I’d like to add some caching support at some point.

Finally, and most notably, ZX2C4 Music no longer hangs when loading giant lists. It now loads 50 items at a time, and polls the location of the scrollbar every 100 milliseconds, and if it is close to the bottom, it requests the next 50 items. Polling is not ideal, but JavaScript does not have scroll events for divs. The pagination is implemented using MySQL’s LIMIT and OFFSET features. The display code took quite a bit of reworking and might still be a little buggy. Do try it out. Internet Explorer requires a special case because of its lack of support for writing to tables’ innerHTML, and Microsoft refuses to fix it. When adding an entire list to the download basket, it takes the time to download and display every item in the query, like the old behavior, and this may introduce some bugs. For the most part though, scrolling auto-pagination support is generally pretty slick.

The download basket/zip feature is no longer capped at 200 songs, as it no longer needs to call an external zip program and store the zip file temporarily. In pure php, I’ve written a custom on-the-fly zip file streamer, which works a lot faster.

As always, if you have suggestions, leave a comment below. If you’d like to download the latest HEAD of ZX2C4 Music, you can browse the repository here or download a tar of it here. Next on the list are HTML5 <audio> element support for web app streaming, Amarok plugin, update script, and maybe a revamped interface.

Here’s a curious problem I’ve come across: There are N columns in a table of width W, with each column having content that requires a maximum width of M₁, M₂, M₃, … , M_N, where M₁ + M₂ + M₃ + … + M_N > W. Find an optimal size, O₁, O₂, O₃, … , O_N, for all columns in the table, where O₁ + O₂ + O₃ + … + O_N = W, and where for all i between 1 and N, O_i / W ≤ R, where R is an arbitrary ratio less than 1 and greater than 0. That is to say, optimally sized means each O_i / W = min(R, M_i / (M₁ + M₂ + M₃ + … + M_N)), but when the min function chooses its first argument, the extra space, ([second argument] – [first argument]) * W, needs to be proportionally distributed to the remaining O_j, where j is between 1 and N and does not equal i, and where “proportionally” means related to the proportions of M_j / (M₁ + M₂ + M₃ + … + M_N). However, proportionally distributing this excess to the remaining columns may push a remaining column’s ratio over R, which means some of that excess might further have to be redistributed.

The iterative approach to this problem is easy, but I am interested in determining a non-iterative solution to finding all of the O_i, where I simply have a formula O_i = [yada yada yada].

Here’s code for the iterative solution when applied to columns of a QTreeView, with N = 3 and R = .42, which is derived from my AutoSizingList class of ZMusicPlayer. It uses QTreeView’s sizeHintForColumn to determine M_i.

So essentially, the problem is that the do-while on lines 18 and 41 should be eliminated. It is required in the first place because when proportionally redistributing the difference between the arguments of the min function (outlined in the first paragraph), the ratios of the columns receiving this extra width may exceed R, which means another iteration must be done to readjust. Anyone have a non-iterative solution? Also, to the Qt experts out there, why is the hack required on line 49?

I am interested both in a practical Qt approach and a mathematical approach, the latter being more interesting. Doesn’t this seem like functionality that aught to already be a part of Qt?

Update: A conversation with a friend over AIM has produced a plain-English explanation in the form of a dialogue of the above problem.

This post is a follow up to Introducing ZX2C4 Music.

Update: source code available here.

I have just finished generalizing aspects of ZX2C4 Music so that it’s installable on a variety of different servers. I have no experience with releasing PHP apps to the general public, so I’d appreciate some feedback on the installation process. You can download the tarball here. Be sure to read README.txt.

Update: source code available here.

A few months ago I switched website hosts from Netfirms to Site5, because Site5 had a good deal for a plan with unlimited bandwidth and disk space. The first thing I did was upload my entire music collection.

To access all of my music remotely via any internet-connected web browser, I wrote ZX2C4 Music, which is password protected to avoid the law, but if you’d like to view the interface just for curiosity, ask me in the comments section, and I’ll e-mail you a password. It uses PHP/MySQL for managing the music, hashing each file with an sha1, TagLib for reading tags, and JavaScript/HTML as an interface:

Search queries are done with AJAX, and playing is done with Flash, if available; otherwise it defaults to browser plug-ins. Soon I should add HTML5′s <audio> element support. Since Flash only supports MP3, the php backend optionally transcodes non-mp3 songs on the fly by using ffmpeg. Songs can be downloaded in zipped bundles by using the download basket feature. The web interface still needs some work, most notably scrolling-pagination for the song table, but it’s definitely usable. Many have pointed my attention to Ampache, but I found it too big and overwhelming. You can view the source code here.

Of course, the next step was writing a Qt or KDE application that interfaces directly with the web backend using Phonon. Meet ZMusicPlayer:

It downloads and displays a compressed and sorted xml listing of all the songs and their sha1s. The columns of the list automatically size optimally using an awesome algorithm that still needs some tweaking (why is subtracting 40 required on line 87?). Suggestions?

It plays the songs by passing the appropriate QUrl to Phonon, and this is where the trouble begins. The xine backend on KDE 4.1.2 just skips one song to another most of the time, and when it does miraculously play, seeking (via HTTP partial requests) is unavailable. The headers for each of the server responses for song file requests provide the appropriate parameters for HTTP seeking. Maybe this has already been fixed in trunk, but if not, I aught to investigate the problem as soon as I switch my 4.1.2 desktop completely to trunk. GStreamer with Qt 4.4 allows for proper streaming if a GStreamer HTTP plug-in is installed (gst-plugins-good includes a wrapper plugin for libsoup, which works, for those who don’t want to install the gnome vfs plugin), which is understandable. However, seeking only works for mp3 files; m4a files play but cannot seek, even though the pertinent response headers are the same for both file types. On the Windows backend, the seeking situation is hopeless, and on the OS X backend, songs do not play at all. Also, xine is the only one that emits the proper buffering signals. On some setups though, some of these problems go away. I still need to do some more thorough debugging.

If you’d like to download and build ZMusicPlayer, you can browse the source, clone the repository with git clone http://git.zx2c4.com/zmusicplayer.git, or download a tarball. Depending on your package setup, you may have to tinker with the includes for the phonon headers. I’d love to hear some suggestions, so leave comments below. Once I stabilize the Qt code, I’d like to develop some optional KDE extensions, particularly integration with the KDE’s keyboard shortcuts.

Also: I’ve switched from blogging on kdedevelopers.org to my own WordPress blog so that anyone can post comments without requiring an approved account. So, comment away. If you wanted to comment on my first post, but were unable to, you can now comment here. To comment on this post, use the link below.

Update Oct 25, 3:31pm: Several of you have e-mailed me to say that the browser hangs when loading a unfiltered giant collection. This is indeed the case, as no current browser is able to write 10,000 rows to a table in a reasonable amount of time. This is why above I speak of “scrolling-pagination”, which means that the table would load 100 or so rows at a time, and then auto-populate the remaining rows in 100 row increments every time the user scrolled to near the end.