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• SNES Hardware Compression

  16 juin 2011, par Multimedia Mike — Game Hacking

  I was browsing the source code for some Super Nintendo Entertainment System (SNES) emulators recently. I learned some interesting things about compression hardware. I had previously uncovered one compression algorithm used in an SNES title but that was implemented in software.

  SNES game cartridges — being all hardware — were at liberty to expand the hardware capabilities of the base system by adding new processors. The most well-known of these processors was the Super FX which allows for basic polygon graphical rendering, powering such games as Star Fox. It was by no means the only such add-on processor, though. Here is a Wikipedia page of all the enhancement chips used in assorted SNES games. A number of them mention compression and so I delved into the emulators to find the details :

  • The Super FX is listed in Wikipedia vaguely as being able to decompress graphics. I see no reference to decompression in emulator source code.
  • DSP-3 emulation source code makes reference to LZ-type compression as well as tree/symbol decoding. I’m not sure if the latter is a component of the former. Wikipedia lists the chip as supporting "Shannon-Fano bitstream decompression."
  • Similar to Super FX, the SA-1 chip is listed in Wikipedia as having some compression capabilities. Again, either that’s not true or none of the games that use the chip (notably Super Mario RPG) make use of the feature.
  • The S-DD1 chip uses arithmetic and Golomb encoding for compressing graphics. Wikipedia refers to this as the ABS Lossless Entropy Algorithm. Googling for further details on that algorithm name yields no results, but I suspect it’s unrelated to anti-lock brakes. The algorithm is alleged to allow Star Ocean to smash 13 MB of graphics into a 4 MB cartridge ROM (largest size of an SNES cartridge).
  • The SPC7110 can decompress data using a combination of arithmetic coding and Z-curve/Morton curve reordering.

  No, I don’t plan to implement codecs for these schemes. But it’s always comforting to know that I could.

  Not directly a compression scheme, but still a curious item is the MSU1 concept put forth by the bsnes emulator. This is a hypothetical coprocessor implemented by bsnes that gives an emulated cartridge access to a 4 GB address space. What to do with all this space ? Allow for the playback of uncompressed PCM audio as well as uncompressed video at 240x144x256 colors @ 30 fps. According to the docs and the source code, the latter feature doesn’t appear to be implemented, though ; only the raw PCM playback.

• I only have two presets for ffmpeg x264 in ubuntu 11.04

  17 octobre 2012, par Mr X Colombia

  I'me trying to install (compile) ffmpeg for ubuntu 11.04 by following this guide :

  https://ffmpeg.org/trac/ffmpeg/wiki/UbuntuCompilationGuide

  Overall it works. Except for some errors with checkinstall due to numbering, which i resolved with this :

  http://judsonsnotes.com/notes/index.php?option=com_content&view=section&layout=blog&id=3&Itemid=54&limitstart=40

  I'd say it was installed ok.

  But when trying to encode some video with -vpre lossless_slow i get this error :

  File for preset lossless_slow not found.

  And in fact it doesn't exists. All i have is this :

  /usr/local/share/ffmpeg:
  
  libvpx-1080p50_60.ffpreset
  
  libvpx-1080p.ffpreset
  
  libvpx-360p.ffpreset
  
  libvpx-720p50_60.ffpreset
  
  libvpx-720p.ffpreset
  
  libx264-ipod320.ffpreset
  
  libx264-ipod640.ffpreset

  Where are all the other presets ? in google usually people have many more presets than i do. What did i do wrong ?

  From this post i'd say that they shopuld be there : http://git.videolan.org/?p=ffmpeg.git ;a=commit ;h=4b82e3cedcfc9871671bb613cd979de6995dcb4e

  Thanks a lot !

• Nomenclature #3465 : Nouvelle balise : #LOGO

  18 février 2021, par cedric -

  oué j’ai quand même un peu de réserves vis à vis d’un code stocké dans un wiki depuis 2 ans et qui a pas servi.
  A moins que ce soit quelque part dans un plugin ?
  bref faudrait trouver quelqu’un qui l’a fait marché et qui peut attester que c’est utilisable.

  Ou le mettre dans bonux ou un autre plugin en rodage...