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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.

• What are the differences between FFmpeg and Libav ? [closed]

  16 septembre 2012, par Ken

  According to the first comment for this question, and i quote

  "Libraries with this name are provided from both the FFmpeg project
  and the Libav project, but they are mutually incompatible". So I think
  the answer depends on which libavcodec do you want to use.

  by user aland and wikipedia

  What are the differences that exist between this 2 projects ?

  I'm interested in video and audio encoding to H/X264, Mp3 and AAC with Mp4/Mkv containers ; but more importantly i would like to start with a reliable and up to date library with a permissive license and widely supported on as many platforms as possible.

• Adding flv header to an .flv.ser file

  15 mai 2014, par wrahool

  I am using Red5 Server version 1.0.2 to record video and audio from an AS3 application. The problem is, when the server shuts down unexpectedly, the .flv.ser temporary file remains.

  I read here that to make an .flv from a temporary .flv.ser file,

  Add the FLV header to it, that’s basically what the .ser file is missing ; it is only audio and video data.

  This Wikipedia page gives an idea of how an flv header looks like.

  Does anyone know how to add flv headers to such a file ? This answer gives the implementation of the flv header, but I’m not sure how to use it.