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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.

• FFMPEG - force webm clusters duration [closed]

  1er avril 2021, par Vlad Sineok

  in short, i'm modifying a game that uses a VP8 video format.
the original videos are at 25 fps and have all clusters of nice and perfect duration 0.96 seconds and contain 25 blocks each (except for that last cluster, which usually varies). also every cluster starts with a keyframe. (all that information i gathered using webm_info from google's libwebm repo)

  


  unless all of the requirements are met, the game struggles to play the webm file smoothly, so my own webm files stutter most of the time, because ffmpeg fails to create the correct clusters and mkclean doesn't help either.
so my question is : how would i force ffmpeg to make all clusters have that perfect duration ?
here's what my command currently looks like

  


  for %%f in (*.webm) do (
ffmpeg -y -i %%f -vcodec libvpx -cpu-used 1 -pass 1 -reserve_index_space 16384 -fflags +genpts -crf 15 -slices 8 -g 25 -keyint_min 25 -vprofile 1 -auto-alt-ref 1 -arnr-maxframes 5 -arnr-strength 3 -deadline good -vf scale=512:384,setsar=1:1 -vb 4000k -an -r 25 -movflags use_metadata_tags -f webm NUL && ^
ffmpeg -y -i %%f -vcodec libvpx -cpu-used 1 -pass 2 -reserve_index_space 16384 -fflags +genpts -crf 15 -slices 8 -g 25 -keyint_min 25 -vprofile 1 -auto-alt-ref 1 -arnr-maxframes 5 -arnr-strength 3 -deadline good -vf scale=512:384,setsar=1:1 -vb 4000k -an -r 25 -movflags use_metadata_tags -f webm %%~nf.webm
)


  


• how to integrate c header files of ffmpeg into Xcode 9.2 using objective C

  14 mars 2016, par Nirbhay

  I am facing the problem while integrating the ffmpeg library into my Xcode project. I have successfully configure ffmpeg and lame library from terminal. Only I encounter the problem in the next i.e interating the ffmpeg library into my Xcode project.. Please help !!