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• Re-solving My Search Engine Problem

  28 juillet 2012, par Multimedia Mike — General, swish-e

  14 years ago, I created a web database of 8-bit Nintendo Entertainment System games. To make it useful, I developed a very primitive search feature.

  A few months ago, I decided to create a web database of video game music. To make it useful, I knew it would need to have a search feature. I realized I needed to solve the exact same problem again.

  Requirements
  The last time I solved this problem, I came up with an excruciatingly naïve idea. Hey, it worked. I really didn’t want to deploy the same solution again because it felt so silly the first time. Surely there are many better ways to solve it now ? Many different workable software solutions that do all the hard work for me ?

  The first time I attacked this, it was 1998 and hosting resources were scarce. On my primary web host I was able to put static HTML pages, perhaps with server side includes. The web host also offered dynamic scripting capabilities via something called htmlscript (a.k.a. MIVA Script). I had a secondary web host in my ISP which allowed me to host conventional CGI scripts on a Unix host, so that’s where I hosted the search function (Perl CGI script accessing a key/value data store file).

  Nowadays, sky’s the limit. Any type of technology you want to deploy should be tractable. Still, a key requirement was that I didn’t want to pay for additional hosting resources for this silly little side project. That leaves me with options that my current shared web hosting plan allows, which includes such advanced features as PHP, Perl and Python scripts. I can also access MySQL.

  Candidates
  There are a lot of mature software packages out there which can index and search data and be plugged into a website. But a lot of them would be unworkable on my web hosting plan due to language or library package limitations. Further, a lot of them feel like overkill. At the most basic level, all I really want to do is map a series of video game titles to URLs in a website.

  Based on my research, Lucene seems to hold a fair amount of mindshare as an open source indexing and search solution. But I was unsure of my ability to run it on my hosting plan. I think MySQL does some kind of full text search, so I could have probably made a solution around that. Again, it just feels like way more power than I need for this project.

  I used Swish-e once about 3 years ago for a little project. I wasn’t confident of my ability to run that on my server either. It has a Perl API but it requires custom modules.

  My quest for a search solution grew deep enough that I started perusing a textbook on information retrieval techniques in preparation for possibly writing my own solution from scratch. However, in doing so, I figured out how I might subvert an existing solution to do what I want.

  Back to Swish-e
  Again, all I wanted to do was pull data out of a database and map that data to a URL in a website. Reading the Swish-e documentation, I learned that the software supports a mode specifically tailored for this. Rather than asking Swish-e to index a series of document files living on disk, you can specify a script for Swish-e to run and the script will generate what appears to be a set of phantom documents for Swish-e to index.
  

  When I ’add’ a game music file to the game music website, I have a scripts that scrape the metadata (game title, system, song titles, composers, company, copyright, the original file name on disk, even the ripper/dumper who extracted the chiptune in the first place) and store it all in an SQLite database. When it’s time to update the database, another script systematically generates a series of pseudo-documents that spell out the metadata for each game and prefix each document with a path name. Searching for a term in the index returns a lists of paths that contain the search term. Thus, it makes sense for that path to be a site URL.

  But what about a web script which can search this Swish-e index ? That’s when I noticed Swish-e’s C API and came up with a crazy idea : Write the CGI script directly in C. It feels like sheer madness (or at least the height of software insecurity) to write a CGI script directly in C in this day and age. But it works (with the help of cgic for input processing), just as long as I statically link the search script with libswish-e.a (and libz.a). The web host is an x86 machine, after all.

  I’m not proud of what I did here— I’m proud of how little I had to do here. The searching CGI script is all of about 30 lines of C code. The one annoyance I experienced while writing it is that I had to consult the Swish-e source code to learn how to get my search results (the "swishdocpath" key — or any other key — for SwishResultPropertyStr() is not documented). Also, the C program just does the simplest job possible, only querying the term in the index and returning the results in plaintext, in order of relevance, to the client-side JavaScript code which requested them. JavaScript gets the job of sorting and grouping the results for presentation.

  Tuning the Search
  Almost immediately, I noticed that the search engine could not find one of my favorite SNES games, U.N. Squadron. That’s because all of its associated metadata names Area 88, the game’s original title. Thus, I had to modify the metadata database to allow attaching somewhat free-form tags to games in order to compensate. In this case, an alias title would show up in the game’s pseudo-document.

  Roman numerals are still a thorn in my side, just as they were 14 years ago in my original iteration. I dealt with it back then by converting all numbers to Roman numerals during the index and searching processes. I’m not willing to do that for this case and I’m still looking for a good solution.

  Another annoying problem deals with Mega Man, a popular franchise. The proper spelling is 2 words but it’s common for people to mash it into one word, Megaman (see also : Spider-Man, Spiderman, Spider Man). The index doesn’t gracefully deal with that and I have some hacks in place to cope for the time being.

  Positive Results
  I’m pleased with the results so far, and so are the users I have heard from. I know one user expressed amazement that a search for Castlevania turned up Akumajou Densetsu, the Japanese version of Castlevania III : Dracula’s Curse. This didn’t surprise me because I manually added a hint for that mapping. (BTW, if you are a fan of Castlevania III, definitely check out the Akumajou Densetsu soundtrack which has an upgraded version of the same soundtrack using special audio channels.)

  I was a little more surprised when a user announced that searching for ’probotector’ correctly turned up Contra : Hard Corps. I looked into why this was. It turns out that the original chiptune filename was extremely descriptive : "Contra - Hard Corps [Probotector] (1994-08-08)(Konami)". The filenames themselves often carry a bunch of useful metadata which is why it’s important to index those as well.

  And of course, many rippers, dumpers, and taggers have labored for over a decade to lovingly tag these songs with as much composer information as possible, which all gets indexed. The search engine gets a lot of compliments for its ability to find many songs written by favorite composers.

• Adding A New System To The Game Music Website

  1er août 2012, par Multimedia Mike — General

  At first, I was planning to just make a little website where users could install a Chrome browser extension and play music from old 8-bit NES games. But, like many software projects, the goal sort of ballooned. I created a website where users can easily play old video game music. It doesn’t cover too many systems yet, but I have had individual requests to add just about every system you can think of.

  The craziest part is that I know it’s possible to represent most of the systems. Eventually, it would be great to reach Chipamp parity (a combination plugin for Winamp that packages together plugins for many of these chiptunes). But there is a process to all of this. I have taken to defining a number of phases that are required to get a new system covered.

  Phase 0 informally involves marveling at the obscurity of some of the console systems for which chiptune collections have evolved. WonderSwan ? Sharp X68000 ? PC-88 ? I may be viewing this through a terribly Ameri-centric lens. I’ve at least heard of the ZX Spectrum and the Amstrad CPC even if I’ve never seen either.

  No matter. The goal is to get all their chiptunes cataloged and playable.

  Phase 1 : Finding A Player
  The first step is to find a bit of open source code that can play a particular format. If it’s a library that can handle many formats, like Game Music Emu or Audio Overload SDK, even better (probably). The specific open source license isn’t a big concern for me. I’m almost certain that some of the libraries that SaltyGME currently mixes are somehow incompatible, license-wise. I’ll worry about it when I encounter someone who A) cares, and B) is in a position to do something about it. Historical preservation comes first, and these software libraries aren’t getting any younger (I’m finding some that haven’t been touched in a decade).

  Phase 2 : Test Program
  The next phase is to create a basic test bench program that sends a music file into the library, generates a buffer of audio, and shoves it out to the speakers via PulseAudio’s simple API (people like to rip on PulseAudio, but its simple API really lives up to its name and requires pages less boilerplate code to play a few samples than ALSA).

  Phase 3 : Plug Into Web Player
  After successfully creating the test bench and understanding exactly which source files need to be built, the next phase is to hook it up to the main SaltyGME program via the ad-hoc plugin API I developed. This API requires that a player backend can, at the very least, initialize itself based on a buffer of bytes and generate audio samples into an array of 16-bit numbers. The API also provides functions for managing files with multiple tracks and toggling individual voices/channels if the library supports such a feature. Having the test bench application written beforehand usually smooths out this step.

  But really, I’m just getting started.

  Phase 4 : Collecting A Song Corpus
  Then there is the matter of staging a collection of songs for a given system. It seems like it would just be a matter of finding a large collection of songs for a given format, downloading them in bulk, and mirroring them. Honestly, that’s the easy part. People who are interested in this stuff have been lovingly curating massive collections of these songs for years (see SNESmusic.org for one of the best examples, and they also host a torrent of all their music for really quick and easy hoarding).
  
  In my drive to make this game music website more useful for normal people, the goal is to extract as much metadata as possible to make searching better, and to package the data so that it’s as convenient as possible for users. Whenever I seek to add a new format to the collection, this is the phase where I invariably find that I have to fundamentally modify some of the assumptions I originally made in the player.

  First, there were the NES Sound Format (NSF) files, the original format I wanted to play. These are files that have any number of songs packed into a single file. Playback libraries expose APIs to jump to individual tracks. So the player was designed around that. Game Boy GBS files also fall into this category but present a different challenge vis-à-vis metadata, addressed in the next phase.

  Then, there were the SPC files. Each SPC file is its own song and multiple SPC files are commonly bundled as RAR files. Not wanting to deal with RAR, or any format where I interacted with a general compression API to pull a few files out, I created a custom resource format (inspired by so many I have studied and documented) and compressed it with a simpler compression API. I also had to modify some of the player’s assumptions to deal with this archive format. Genesis VGMs, bundled either in .zip or .7z, followed the same model as SPC in RAR.

  Then it was suggested that I attempt to bring SaltyGME closer to feature parity with Chipamp, rather than just being a Chrome browser frontend for Game Music Emu. When I studied the Portable Sound Format (PSF), I realized it didn’t fit into the player model I already had. PSF uses a sort of shared library model for code execution and I developed another resource archive format to cope with it. So that covers quite a few formats.

  One more architecture challenge arose when I started to study one of the prevailing metadata formats, explained in the next phase.

  Phase 5 : Metadata
  Finally, for the collections to really be useful, I need to harvest that juicy metadata for search and presentation.

  I have created a series of programs and scripts to scrape metadata out of these music files and store it all in a database that drives the website and search engine. I recognize that it’s no good to have a large corpus of songs with minimal metadata and while importing bulk quantities of music, the scripts harshly reject songs that have too little metadata.

  Again, challenges abound. One of the biggest challenges I’m facing is the peculiar quasi-freeform metadata format that emerged as .m3u that takes a form similar to :

  #################################################################
  #
  # GRADIUS2
  # (c) KONAMI  by Furukawa Motoaki, IKACHAN
  #
  #################################################################
  nemesis2.kss::KSS,62,[Nemesis2] (Opening),2:23,,0
  
  nemesis2.kss::KSS,61,[Nemesis2] (Start),7,,0
  
  nemesis2.kss::KSS,43,[Nemesis2] (Air Battle),34,0-
  
  nemesis2.kss::KSS,44,[Nemesis2] (1st. BGM),51,0-
  
  [...]
  

  A lot of file formats (including Game Boy GBS mentioned earlier) store their metadata separately using this format. I have some ideas about tools I can use to help me process this data but I’m pretty sure each one will require some manual intervention.

  As alluded to in phase 4, .m3u presents another architectural challenge : Notice the second field in the CSV .m3u data. That’s a track number. A player can’t expect every track in a bundled chiptune file to be valid, nor to be in any particular order. Thus, I needed to alter the architecture once more to take this into account. However, instead of modifying the SaltyGME player, I simply extended the metadata database to include a playback order which, by default, is the same as the track order but can also accommodate this new issue. This also has the bonus of providing a facility to exclude playback of certain tracks. This comes in handy for many PSF archives which tend to include files that only provide support for other files and aren’t meant to be played on their own.

  Bright Side
  The reward for all of this effort is that the data lands in a proper database in the end. None of it goes back into the chiptune files themselves. This makes further modification easier as all of the data that is indexed and presented on the site comes from the database. Somewhere down the road, I should probably create an API for accessing this metadata.

• cvCaptureFromFile always returns NULL, Visual Studio 2005

  14 septembre 2012, par user1671173

  I've got a problem with the cvCaptureFromFile function. It always returns NULL. I've done some research on the internet and I've added PATH to ffmpeg's "bin" directory.
  But it's still the same. So I've tried to open the desired file with ffplay.exe. It returns an error which says "Invalid data found when processing an input". It is a "mjpg" file, which should be played with ffmpeg. Then I tried the same with some "mpg" file.
  Now the message is "no such file or directory" which is not true, because the file is in the place. What else should I do ?
  The files all right with Media-Player and VLC player.
  Please help !