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• FFmpeg framerate parameter

  24 avril 2020, par mentalmushroom

  I am confused by the FFmpeg framerate parameter. As far as I understand the docs and wiki, it sets the number of frames per second for the input (and the output unless -r option is specified). In fact, when I set the framerate to 1, the video is being played pretty much at its normal speed (25-30, but definitely not 1 frame per second as expected). Setting framerate to 2 makes it play around twice as fast (not 2 frames per second).

  



  To give a little bit more details, there is a python script which reads a video sample frame-by-frame as fast as it can and outputs these frames immediately to FFmpeg :

  



  python main.py -i myvideo.mp4 | ffmpeg -v warning -f rawvideo -pixel_format bgr24 -video_size 768x432 -framerate 2 -i - http://0.0.0.0:3004/fac.ffm


  



  What could be the reason for such behavior ?

  


• Evolution #3017 : Gestion des versions de plugins

  30 septembre 2016, par Franck Dalot

  Ce commit (il y a d’autre cas de borne max dans la zone) http://zone.spip.org/trac/spip-zone/changeset/99750/_plugins_/clients/trunk vient de me refaire pensé à ce ticket :-)
  En faite, je ne suis pas certain qu’un simple message soit suffisant, car prenant le cas présent, sauf à savoir que le plugin client "necessite" contact et organisation l’utilisateur "basique" ne va pas savoir quoi faire...
  Alors que si spip fait un stockage de l’information, il pourrait "empêcher" la mise à jour de c&o en indiquant que cela désactivera le plugin client en version x.y.z car necessitant contacte et organisation en version maximum x.y.z
  Ainsi si la personne fait quand même la mise à jour, elle saura les conséquences avec un minimum de précision !

  Par contre, il y a un autre cas ou je ne sais pas s’il est possible de faire quelque chose.
  Imaginons qu’une personne à le plugin "client" qui necessite donc contacte et organisation version 2 ; mais que cette même personne souhaite faire l’installation d’un autre plug mais qui demanderait cette fois contacte et organisation en version 3, comme cela se passerait au niveau des tables, de contacte et organisation si la personne installe les deux versions du plug ????
  Car si la possibilité d’installation de plusieurs versions d’un plug est une bonne idée je ne sais pas si c’est vraiment possible ?

• 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.