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• Dreamcast Archival

  24 mai 2011, par Multimedia Mike — Sega Dreamcast

  Console homebrew communities have always had a precarious relationship with console pirates. The same knowledge and skills useful for creating homebrew programs can usually be parlayed into ripping games and cajoling a console into honoring ripped copies. For this reason, the Dreamcast homebrew community tried hard to distance itself from pirates, rippers, and other unsavory characters.

  
  
  

  Funny how times change. While I toed the same line while I was marginally a part of the community back in the day, now I think I’m performing a service for video game archivists and historians by openly publishing the same information. I know of at least one solution already. But I think it’s possible to do much better.

  Pre-existing Art
  Famed Japanese game hacker BERO (FFmpeg contributors should recognize his name from a number of Dreamcast-related multimedia contributions including CRI ADX and SH-4 optimizations) crafted a program called dreamrip based on KOS’s precursor called libdream. This is the program I used to extract 4XM multimedia files from Alone in the Dark : The New Nightmare.

  Fun facts : The Sega Dreamcast used special optical discs called GD-ROMs. The GD stands for ‘GigaDisc’ which implied that they could hold roughly a gigabyte of data. How long do you think it takes to transfer that much data over a serial cable operating at 115,200 bits/second (on the order of 11 Kbytes/sec) ? I seem to recall entire discs requiring on the order of 27-28 hours to archive.

  If only I possessed some expertise in data compression which might expedite this process.

  KallistiOS’ Unwitting Help
  The KallistiOS (KOS) console-oriented RTOS provides all the software infrastructure necessary for archiving (that’s what we’ll call it in this post) Dreamcast games. KOS exposes the optical disc’s filesystem via the /cd mount point on the VFS. From there, KOS provides functions for communicating with a host computer via ethernet (broadband adapter) or serial line (DC coder’s cable). To this end, KOS exposes another mount point on the VFS named /pc which allows direct access to the host PC’s filesystem.

  Thus, it’s pretty straightforward to use KOS to access the files (or raw sectors) of the Dreamcast disc and then send them over the communication line to the host PC. Simple.

  Compressing Before Transfer
  Right away, I wonder about compiling 3 different compression libraries : libz, libbz2, and liblzma. The latter 2 are exceptionally CPU-intensive to compress. Then again, it doesn’t really matter how long the compressor takes to do its job as long as it can average better than 11 Kbytes/sec on a 200MHz Hitachi SH-4 CPU. KOS can be set up in a preemptive threading mode which means it should be possible to read sectors and compress them while keeping the UART operating at full tilt.

  A 4th compression algorithm should be in play here as well : FLAC. Since some of these discs contain red book CD audio tracks that need archival, lossless audio compression should be useful.

  This post serves as a rough overview for possible future experiments. Readers might have further brainstorms.

• Multimedia Exploration Journal : The Past Doesn’t Die

  12 juillet 2011, par Multimedia Mike — Game Hacking

  New haul of games, new (old) multimedia formats.

  Lords of Midnight
  Check out the box copy scan for Lords of Midnight in MobyGames. In particular, I’d like to call your attention to this little blurb :

  
  
  

  Ahem, "Journey through an immense world — the equivalent of 8 CD-ROMs." Yet, when I procured the game, it only came on a single CD-ROM. It’s definitely a CD-ROM (says so on the disc) and, coming from 1995, certainly predates the earliest DVD-ROMs (which can easily store 8 CD-ROMs on a disc). Thus, I wanted to jump in a see if they were using some phenomenal compression in order to squeeze so much info into 600 or so megabytes.

  I was surprised to see the contents of the disc clocking in at just under 40 megabytes. An intro movie and an outro movie account for 75% of that. Format ? None other than that curious ASCII anomaly, ARMovie/RPL with Escape 122 codec data.

  Cyclemania

  
  
  

  Cyclemania is one of those FMV backdrop action games, but with a motorcycle theme. I had a good feeling I would find some odd multimedia artifacts here and the game didn’t disappoint. The videos are apparently handled using 3-4 discrete files per animation. I’ve documented my cursory guesses and linked some samples at the new MultimediaWiki page.

  Interplay ACMP
  This is unrelated to this particular acquistion, but I was contacted today about audio files harvested from the 1993 DOS game Star Trek : Judgment Rites. The files begin with the ASCII signature "Interplay ACMP Data". This reminds me of Interplay MVE files which begin with the similar string "Interplay MVE File". My theory is that these files use the ACOMP compression format, though I’m still trying to make it fit.

  Wiki and samples are available as usual if you’d like to add your own research.

• How to profile compression speed for a h264 encoder

  25 mai 2018, par Dean

  I’m using nvenc to compress in h264 a video stream. I now have a kinda-working low latency implementation for game streaming purposes but I’m struggling to get reliable profiling results. I’ve been trying to stream a video (so everything is predetermined) via my encoder to the clients in controlled network conditions (e.g. locally). I tried to time average compression times per frame but they’re highly volatile and the numbers I get aren’t that meaningful.

  How are low latency streaming encoders tested for performances ?