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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.

• Android ffmpeg and hardware acceleration

  4 mai 2015, par ApriOri

  I want my video streaming application to utilize hardware acceleration in android.
  I’m limited to udp video broadcasting so I can’t use Android media player, so I plan to use ffmpeg.
  Is there a way to make ffmpeg utilize hardware acceleration on android ?

• Download Partial Video via HTTP (for Remote Thumbnailing)

  13 février 2012, par HuntedC

  I have videos hosted on Amazon S3. I encode them with Zencoder and store a thumbnail for the video then using Zencoder. However, I need a way to generate thumbnails at certain points in the video (i.e. 00:00:03, 00:10:32, 01:40:18) and store them either on S3 or my server.

  ffmpeg allows remote thumbnailing, however it takes a very long time (sometimes several minutes) to get a thumbnail from the middle of a file—I believe this is because it downloads the entire file up to that point to get the thumbnail.

  My plan is to somehow download the header of the video file via HTTP byte-range request, guesstimate the byte range where I should be looking for the thumbnail, download about a second of video from that part of the file via HTTP byte-range request, then save the header and tiny video locally. I pull the thumbnail from that using ffmpeg and delete the temporary video.

  I have no idea on how exactly this would work (I believe the H.264 MP4 files I'm working with have a dynamic length header, for another issue). Any suggestions or better ideas ?

  Edit : To clarify, Zencoder thumbnailing is great, but they only allow thumbnail creation in combination with transcoding. I don't want to transcode my video every time I create a new thumbnail, so I need to do this on my own without Zencoder.