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Spitfire Parade - Crisis
15 mai 2011, par
Mis à jour : Septembre 2011
Langue : English
Type : Audio
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Wired NextMusic
14 mai 2011, par
Mis à jour : Février 2012
Langue : English
Type : Video
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Video d’abeille en portrait
14 mai 2011, par
Mis à jour : Février 2012
Langue : français
Type : Video
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Sintel MP4 Surround 5.1 Full
13 mai 2011, par
Mis à jour : Février 2012
Langue : English
Type : Video
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Carte de Schillerkiez
13 mai 2011, par
Mis à jour : Septembre 2011
Langue : English
Type : Texte
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Publier une image simplement
13 avril 2011, par ,
Mis à jour : Février 2012
Langue : français
Type : Video
Autres articles (41)
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(Dés)Activation de fonctionnalités (plugins)
18 février 2011, parPour gérer l’ajout et la suppression de fonctionnalités supplémentaires (ou plugins), MediaSPIP utilise à partir de la version 0.2 SVP.
SVP permet l’activation facile de plugins depuis l’espace de configuration de MediaSPIP.
Pour y accéder, il suffit de se rendre dans l’espace de configuration puis de se rendre sur la page "Gestion des plugins".
MediaSPIP est fourni par défaut avec l’ensemble des plugins dits "compatibles", ils ont été testés et intégrés afin de fonctionner parfaitement avec chaque (...) -
Le plugin : Podcasts.
14 juillet 2010, parLe problème du podcasting est à nouveau un problème révélateur de la normalisation des transports de données sur Internet.
Deux formats intéressants existent : Celui développé par Apple, très axé sur l’utilisation d’iTunes dont la SPEC est ici ; Le format "Media RSS Module" qui est plus "libre" notamment soutenu par Yahoo et le logiciel Miro ;
Types de fichiers supportés dans les flux
Le format d’Apple n’autorise que les formats suivants dans ses flux : .mp3 audio/mpeg .m4a audio/x-m4a .mp4 (...) -
Les autorisations surchargées par les plugins
27 avril 2010, parMediaspip core
autoriser_auteur_modifier() afin que les visiteurs soient capables de modifier leurs informations sur la page d’auteurs
Sur d’autres sites (7156)
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What Is Ethical SEO & Why Does It Matter ?
7 mai 2024, par Erin -
Adding C64 SID Music
1er novembre 2012, par Multimedia Mike — GeneralI have been working on adding support for SID files — the music format for the Commodore 64 — to the game music website for awhile. I feel a bit out of my element since I’m not that familiar with the C64. But why should I let that slow me down ? Allow me to go through the steps I have previously outlined in order to make this happen.
I need to know what picture should represent the system in the search results page. The foregoing picture should be fine, but I’m getting way ahead of myself.
Phase 1 is finding adequate player software. The most venerable contender in this arena is libsidplay, or so I first thought. It turns out that there’s libsidplay (originally hosted at Geocities, apparently, and no longer on the net) and also libsidplay2. Both are kind of old (libsidplay2 was last updated in 2004). I tried to compile libsidplay2 and the C++ didn’t agree with current version of g++.
However, a recent effort named libsidplayfp is carrying on the SID emulation tradition. It works rather well, notwithstanding the fact that compiling the entire library has a habit of apparently hanging the Linux VM where I develop this stuff.
Phase 2 is to develop a testbench app around the playback library. With the help of the libsidplayfp library maintainers, I accomplished this. The testbench app consistently requires about 15% of a single core of a fairly powerful Core i7. So I look forward to recommendations that I port that playback library to pure JavaScript.
Phase 3 is plug into the web player. I haven’t worked on this yet. I’m confident that this will work since phase 2 worked (plus, I have a plan to combine phases 2 and 3).
One interesting issue that has arisen is that proper operation of libsidplayfp requires that 3 C64 ROM files be present (the, ahem, KERNAL, BASIC interpreter, and character generator). While these are copyrighted ROMs, they are easily obtainable on the internet. The goal of my project is to eliminate as much friction as possible for enjoying these old tunes. To that end, I will just bake the ROM files directly into the player.
Phase 4 is collecting a SID song corpus. This is the simplest part of the whole process thanks to the remarkable curation efforts of the High Voltage SID Collection (HVSC). Anyone can download a giant archive of every known SID file. So that’s a done deal.
Or is it ? One small issue is that I was hoping that the first iteration of my game music website would focus on, well, game music. There is a lot of music in the HVSC that are original compositions or come from demos. The way that the archive is organized makes it difficult to automatically discern whether a particular SID file comes from a game or not.
Phase 5 is munging the metadata. The good news here is that the files have the metadata built in. The not-so-great news is that there isn’t quite as much as I might like. Each file is tagged with title, author, and publisher/copyright. If there is more than one song in a file, they all have the same metadata. Fortunately, if I can import them all into my game music database, there is an opportunity to add a lot more metadata.
Further, there is no play length metadata for these files. This means I will need to set each to a default length like 2 minutes and do something like I did before in order to automatically determine if any songs terminate sooner.
Oddly, the issue I’m most concerned about is character encoding. This is the first project for which I’m making certain that I understand character encoding since I can’t reasonably get away with assuming that everything is ASCII. So far, based on the random sampling of SID files I have checked, there is a good chance of encountering metadata strings with characters that are not in the lower ASCII set. From what I have observed, these characters map to Unicode code points. So I finally get to learn about manipulating strings in such a way that it preserves the character encoding. At the very least, I need Python to rip the strings out of the binary SID files and make sure the Unicode remains intact while being inserted into an SQLite3 database.
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Grand Unified Theory of Compact Disc
1er février 2013, par Multimedia Mike — GeneralThis is something I started writing about a decade ago (and I almost certainly have some of it wrong), back when compact discs still had a fair amount of relevance. Back around 2002, after a few years investigating multimedia technology, I took an interest in compact discs of all sorts. Even though there may seem to be a wide range of CD types, I generally found that they’re all fundamentally the same. I thought I would finally publishing something, incomplete though it may be.
Physical Perspective
There are a lot of ways to look at a compact disc. First, there’s the physical format, where a laser detects where pits/grooves have disturbed the smooth surface (a.k.a. lands). A lot of technical descriptions claim that these lands and pits on a CD correspond to ones and zeros. That’s not actually true, but you have to decide what level of abstraction you care about, and that abstraction is good enough if you only care about the discs from a software perspective.Grand Unified Theory (Software Perspective)
Looking at a disc from a software perspective, I have generally found it useful to view a CD as a combination of a 2 main components :- table of contents (TOC)
- a long string of sectors, each of which is 2352 bytes long
I like to believe that’s pretty much all there is to it. All of the information on a CD is stored as a string of sectors that might be chopped up into a series of anywhere from 1-99 individual tracks. The exact sector locations where these individual tracks begin are defined in the TOC.
Audio CDs (CD-DA / Red Book)
The initial purpose for the compact disc was to store digital audio. The strange sector size of 2352 bytes is an artifact of this original charter. “CD quality audio”, as any multimedia nerd knows, is formally defined as stereo PCM samples that are each 16 bits wide and played at a frequency of 44100 Hz.
(44100 audio frames / 1 second) * (2 samples / audio frame) * (16 bits / 1 sample) * (1 byte / 8 bits) = 176,400 bytes / second (176,400 bytes / 1 second) / (2352 bytes / 1 sector) = 75
75 is the number of sectors required to store a single second of CD-quality audio. A single sector stores 1/75th of a second, or a ‘frame’ of audio (though I think ‘frame’ gets tossed around at all levels when describing CD formats).
The term “red book” is thrown around in relation to audio CDs. There is a series of rainbow books that define various optical disc standards and the red book describes audio CDs.
Basic Data CD-ROMs (Mode 1 / Yellow Book)
Somewhere along the line, someone decided that general digital information could be stored on these discs. Hence, the CD-ROM was born. The standard model above still applies– TOC and string of 2352-byte sectors. However, it’s generally only useful to have a single track on a CD-ROM. Thus, the TOC only lists a single track. That single track can easily span the entire disc (something that would be unusual for a typical audio CD).While the model is mostly the same, the most notable difference between and audio CD and a plain CD-ROM is that, while each sector is 2352 bytes long, only 2048 bytes are used to store actual data payload. The remaining bytes are used for synchronization and additional error detection/correction.
At least, the foregoing is true for mode 1 / form 1 CD-ROMs (which are the most common). “Mode 1″ CD-ROMs are defined by a publication called the yellow book. There is also mode 1 / form 2. This forgoes the additional error detection and correction afforded by form 1 and dedicates 2336 of the 2352 sector bytes to the data payload.
CD-ROM XA (Mode 2 / Green Book)
From a software perspective, these are similar to mode 1 CD-ROMs. There are also 2 forms here. The first form gives a 2048-byte data payload while the second form yields a 2324-byte data payload.Video CD (VCD / White Book)
These are CD-ROM XA discs that carry MPEG-1 video and audio data.Photo CD (Beige Book)
This is something I have never personally dealt with. But it’s supposed to conform to the CD-ROM XA standard and probably fits into my model. It seems to date back to early in the CD-ROM era when CDs were particularly cost prohibitive.Multisession CDs (Blue Book)
Okay, I admit that this confuses me a bit. Multisession discs allow a user to burn multiple sessions to a single recordable disc. I.e., burn a lump of data, then burn another lump at a later time, and the final result will look like all the lumps were recorded as the same big lump. I remember this being incredibly useful and cost effective back when recordable CDs cost around US$10 each (vs. being able to buy a spindle of 100 CD-Rs for US$10 or less now). Studying the cdrom.h file for the Linux OS, I found a system call named CDROMMULTISESSION that returns the sector address of the start of the last session. If I were to hypothesize about how to make this fit into my model, I might guess that the TOC has some hint that the disc was recorded in multisession (which needs to be decided up front) and the CDROMMULTISESSION call is made to find the last session. Or it could be that a disc read initialization operation always leads off with the CDROMMULTISESSION query in order to determine this.I suppose I could figure out how to create a multisession disc with modern software, or possibly dig up a multisession disc from 15+ years ago, and then figure out how it should be read.
CD-i
This type puzzles my as well. I do have some CD-i discs and I thought that I could read them just fine (the last time I looked, which was many years ago). But my research for this blog post has me thinking that I might not have been seeing the entire picture when I first studied my CD-i samples. I was able to see some of the data, but sources indicate that only proper CD-i hardware is able to see all of the data on the disc (apparently, the TOC doesn’t show all of the sectors on disc).Hybrid CDs (Data + Audio)
At some point, it became a notable selling point for an audio CD to have a data track with bonus features. Even more common (particularly in the early era of CD-ROMs) were computer and console games that used the first track of a disc for all the game code and assets and the remaining tracks for beautifully rendered game audio that could also be enjoyed outside the game. Same model : TOC points to the various tracks and also makes notes about which ones are data and which are audio.There seems to be 2 distinct things described above. One type is the mixed mode CD which generally has the data in the first track and the audio in tracks 2..n. Then there is the enhanced CD, which apparently used multisession recording and put the data at the end. I think that the reasoning for this is that most audio CD player hardware would only read tracks from the first session and would have no way to see the data track. This was a positive thing. By contrast, when placing a mixed-mode CD into an audio player, the data track would be rendered as nonsense noise.
Subchannels
There’s at least one small detail that my model ignores : subchannels. CDs can encode bits of data in subchannels in sectors. This is used for things like CD-Text and CD-G. I may need to revisit this.In Summary
There’s still a lot of ground to cover, like how those sectors might be formatted to show something useful (e.g., filesystems), and how the model applies to other types of optical discs. Sounds like something for another post.