It’s been some time since na_game_tool release and I’ve finally started working on adding new formats for it again (for v0.4 the goal is to have a hundred of supported formats including a dozen of fresh ones, currently it has only about eighty). And since newly added formats are somewhat remarkable, I decided to talk about them.
Spidy Ani from Imperium Galactica. The name sounded vaguely familiar and indeed I’ve encountered it before. I did not bother to support old sprite format since they are just animations for which you need to know the background image and palette. Version 2 contains both palette and (optionally) audio, making its support much more reasonable. As for the compression, it actually keeps the old RLE method and introduces a new one (where low values mean copy length instead of a literal) plus it adds optional LZSS compression. The best part is that it’s not been reverse engineered by somebody else but it has been documented (in open-ig wiki) as well.
Shadowcaster cutscenes. This is a format used by a game published by Origin, it turned out to be RLE optionally further compressed by LZSS (I shan’t blame you if you see some similarities here). The main difference is that the format contains commands for e.g. playing an external XMI track (or stop playing it). And instead of one palette it can store several and switch between them arbitrarily.
Castles 2 (CD version) greyscale video. This one is very special: the game has colour cutscenes in Interplay MVE format (usually with castles) but beside that it apparently has some greyscale animations lifted from public domain films. The files have .m extension and start with “BYON PIZZA” string, definitely not hinting at Byon Garrabrant, who was the lead programmer of that game.
It was extremely hard to read the binary specification for it as the executable stored that code and data in executable overlay. That means that it was in a special part of executable that gets loaded on demand, thus lacking proper references to the data and even functions. Luckily it turned out that I didn’t need it at all.
One of the sequences turned out to be just one black (or white) frame. Seeing that the frame was exactly 1/4th of raw image and filled with 0x40, I decided to calculate a histogram of some other (larger) frame. It turned out that indeed if you output values in 0x00-0x3F range as is and repeat 0x40-0x7F values four times you get exactly full image. Then by looking at the reconstructed image I understood that it codes data in 2×2 blocks (and in inverse mode so 0x00 means white and 0x3F means black). After that figuring out that codes 0x80-0xFF in subsequent frames are used to signal skips was trivial.
That was fun. Hopefully I’ll encounter more interesting formats in the future.
P.S. I’ve also added PI-Video decoding support to NihAV. The codec was used at least in one multimedia encyclopaedia and did some non-conventional things with LZW coding. I’m still not sure that it was a good idea because codec developer may be russian but since I could not find any information about him (or the companies involved beside them being Western European), I’m giving it the benefit of the doubt.
Codecs are too boring, switched working on real production side only. Improving the application of lavfi-preview, with more features like muxing/encoding/seek support, persistent options and similar, improving look and feel, etc..
That’s an important thing too, and if it brings you joy—go ahead.
Back in the day I suggested j-b to leave VLC aside until there’s really important feature to implement and work on a video editor instead. At least he took the first part of my advice…