Sur d’autres sites (4049)

• Game Music Appreciation

  16 juillet 2012, par Multimedia Mike — Game Hacking

  A little over a year ago, I was prototyping a method to leverage Google Chrome’s Native Client technology in order to play old chiptunes (video game music) directly in a web browser. The last time I posted on the matter, I said that I might have something ready for public consumption by the time Google Chrome 21 rolled around. I thought I was being facetious but I wasn’t too far off. Chrome 20 is the current release version as I write this.

  Anyway, I did it : I created a chiptune music player in Native Client by leveraging existing C/C++ libraries such as Game Music Emu, Audio Overload SDK, and Vio2sf. Then I packaged up the player into into a Google Chrome extension and published it on the Chrome Web Store. Then I made a website cataloging as many chiptunes as I could find for 7 different systems :

  http://gamemusic.multimedia.cx/
  

  Check it out if you have any affinity for old game music or you want to hear how music was made using a limited range of bleeps and bloops. Thus far, the site catalogs NES, SNES, Game Boy, Nintendo DS, Genesis, Saturn, and Dreamcast songs. I’m hoping to add support and catalogs for many more systems, though, eventually bringing support in line with the Chipamp plugin for Winamp.

• How does FFmpeg determine the “attached pic” and “timed thumbnails” dispositions of an MP4 track ?

  6 mars, par obskyr

  The Issue

  


  FFmpeg has a concept of “dispositions” – a property that describes the purpose of a stream in a media file. For example, here are the streams in a file I have lying around, with the dispositions emphasized :

  


    Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo,&#xA;fltp, 251 kb/s <strong><em>(default)</em></strong>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Audio&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:1[0x2](und): Video: mjpeg (Baseline) (jpeg / 0x6765706A),&#xA;yuvj420p(pc, bt470bg/unknown/unknown), 1024x1024, 0 kb/s, 0.0006 fps, 3.08 tbr,&#xA;600 tbn <strong><em>(default) (attached pic) (timed thumbnails)</em></strong>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Video&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:2[0x3](und): Data: bin_data (text / 0x74786574)&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Text&#xA;&#xA;  Stream #0:3[0x0]: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/&#xA;unknown), 1024x1024 [SAR 144:144 DAR 1:1], 90k tbr, 90k tbn <strong><em>(attached pic)</em></strong>

  


  However, if I make any modification to this file’s chapter markers using the C++ library MP4v2 (even just re-saving the existing ones : auto f = MP4Modify("test.m4a"); MP4Chapter_t* chapterList; uint32_t chapterCount; MP4GetChapters(f, &chapterList, &chapterCount); MP4SetChapters(f, chapterList, chapterCount); MP4Close(f);), some of these dispositions are removed :

  


    Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo,&#xA;fltp, 251 kb/s <strong><em>(default)</em></strong>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Audio&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:1[0x2](und): Video: mjpeg (Baseline) (jpeg / 0x6765706A),&#xA;yuvj420p(pc, bt470bg/unknown/unknown), 1024x1024, 0 kb/s, 0.0006 fps, 3.08 tbr,&#xA;600 tbn <strong><em>(default)</em></strong> <kbd>← “attached pic” and “timed thumbnails” removed!</kbd>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Video&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:2[0x0]: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/&#xA;unknown), 1024x1024 [SAR 144:144 DAR 1:1], 90k tbr, 90k tbn <strong><em>(attached pic)</em></strong>&#xA;&#xA;  Stream #0:3[0x4](und): Data: bin_data (text / 0x74786574)&#xA;  <kbd>This stream was moved to the end, but that’s intended behavior. It contains chapter titles, and we just edited the chapters.</kbd>&#xA;      Metadata:&#xA;        creation_time   : 2025-03-05T09:56:31.000000Z

  


  It also renders the file unplayable in MPC-HC (but not in VLC !), which is apparently a bug in MP4v2. I’m currently investigating that bug to report and potentially fix it, but that’s a separate issue – in my journey there, I’m wracking my brain trying to understand what it is that MP4v2 changes to make FFmpeg stop reporting the “attached pic” and “timed thumbnails” dispositions. I’ve explored the before-and-afters in MP4 Box, and I can’t for the life of me find which atom it is that differs in a relevant way.

  


  (I’d love to share the files, but unfortunately the contents are under copyright – if anyone knows of a way to remove the audio from an MP4 file without changing anything else, let me know and I’ll upload dummied-out versions. Without them, I can’t really ask about the issue directly. I can at least show you the files’ respective atom trees, but I’m not sure how relevant that is.)

  


  The Question

  


  I thought I’d read FFmpeg’s source code to find out how it determines dispositions for MP4 streams, but of course, FFmpeg is very complex. Could someone who’s more familiar with C and/or FFmpeg’s codebase help me sleuth out how FFmpeg determines dispositions for MP4 files (in particular, “attached pic” and “timed thumbnails”) ?

  


  Some Thoughts…

  


  

  • I figure searching for “attached_pic” might be a good start ?

  


  • Could the MP4 muxer movenc.c be helpful ?

  


  • I’d imagine what we’d really like to look at is the MP4 demuxing process, as it’s during demuxing that FFmpeg determines dispositions from the data in the file. After poring over the code for hours, however, I’ve been utterly unable to find where that happens.

  


  


• FATE’s New Look

  4 août 2010, par Multimedia Mike — FATE Server

  The FATE main page exposes a lot of data. The manner in which it is presented has always been bounded by my extremely limited web development abilities. I wrestled with whether I should learn better web development skills first and allow that to inform any improved design, or focus on the more useful design and invest my web development learning time towards realizing that design.

  Fortunately, Mans solved this conundrum with an elegantly simple solution :

  
  
  

  The top of the page displays a status bar that illustrates — at a glance — how functional the codebase is. The web page source code identifies this as the failometer. It took me a few seconds to recognize what information that status bar was attempting to convey ; maybe it could use a succinct explanation.

  Mini-Book Review
  
  Before Mans took over, I thought about this problem quite a bit. I needed inspiration for creating a better FATE main page and aggregating a large amount of data in a useful, easily-digested form. Looking around the web, I see no shortage of methods for visualizing data. I could start shoehorning FATE data into available methods and see what works. But I thought it would be better to take a step back and think about the best way to organize the data. My first clue came awhile ago in the form of an xkcd comic : Blogofractal. Actually, the clue came from the mouseover text which recommended Edward Tufte’s "The Visual Display of Quantitative Information".

  
  
  

  I ordered this up and plowed through it. It’s an interesting read, to be sure. However, I think it illustrates what a book on multimedia and compression technology would look like if authored by yours truly— a book of technical curiosities from epochs past that discusses little in the way of modern practical application. Tufte’s book showed me lots of examples of infographics from decades and even centuries past, but I never concisely learned exactly how to present data such as FATE’s main page in a more useful form.

  Visualization Blog
  More recently, I discovered a blog called Flowing Data, authored by a statistics Ph.D. candidate who purportedly eats, sleeps, and breathes infographics. The post 11 Ways to Visualize Changes Over Time : A Guide offers a good starting point for creating useful data presentations.

  I still subscribe to and eagerly read Flowing Data. But I might not have as much use for data visualization now that Mans is on FATE duty.