Kostya's Boring Codec World

Since OSQ format requires obtaining a copy of some expensive software of unknown old version, I’ll leave it to somebody else. Meanwhile I’ve looked closer at the AVC format mentioned in the previous post and its relatives.

For those of you who don’t recognize the name immediately, Digital Pictures is the company responsible for some FMV-based action games, including the infamous Night Trap. As I rediscovered previously, the AVC files they use are really SGA files with compression method 0x81 but what about the other formats?

About half of the games I could look at contain an archive occupying most of the CD space, inside that archive are the same AVC files. Other half of the games usually has one or two AVC files with a company logo and one megamovie in various formats. And after some research it turned out to be the same 0x81 compression format but with audio data and varying headers.

And since nobody bothered to document it for The Wiki, I’ll explain it here.
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Since I have nothing better to do as usual, I decided to look at some game formats.

For instance, there’s a game called The Fuel Run promoting a product from a Swiss company supporting russian war crimes. This game has animations in VDO format. VDO file header starts with the string “Artform” and it employs RLE compression, each line of the frame prefixed with its size. What’s funny is that its RLE uses only bottom 6 bits for the run length and top bit is completely unused. For obvious reasons the format is not worthy documenting further.

Or there’s a game called Double Switch, this one has AVC videos. It uses RGB555 palette and 8×8 tiles that depending on opcode may be either coded with one of 25 predefined patterns and 1-7 colours or split into tiles of the smaller size. And only afterwards I decided to look into The Wiki and it seems to match SGA format description (except that this particular format variant is not documented). I don’t know if I should bother writing a decoder for it but with the lack of PC codecs to RE I might try my hoof at console ones instead.

So I decided to look at yet another game at archive.org with an FMV tag. This time it was The Lawnmower Man. It had NXL format that should be a rather unremarkable container with raw video and audio except for one fact: it is EGA full-motion video (320×200, 16 colours, custom palette per each frame). It is the first time I see video being stored in planar form (i.e. for each line first the lowest bits of each colour index value are stored, then bits 1, bits 2 and finally bits 3). Now consider that the format is big-endian (even if DOS version came out reportedly earlier than Mac or SEGA CD versions) and it feels positively weird.

Some of the details I bothered to document are at the usual place (somebody should keep The Wiki alive beside Mike after all).

Sometimes I watch reviews of various old video games (usually of adventure type but not necessarily). This time it was Conquest Earth RTS from 1997 and the reviewer said magic words: “I was not able to extract or play videos with anything”. Okay, you got my attention.

I could find some .rpl files there using Escape 124 codec (yes, Eidos was the publisher, how could you tell?), some standalone .flh files and some flicN.wad archives. Despite the name, the archives turned out to have a footer, i.e. all metadata is stored at the end for a change. The video files seem to be some .flc but mostly .flh.

As one could reasonably expect, it turned out to be yet another hack of the old venerable FLIC format, now with RNCv2 compression. I did not look further to find out whether it’s raw frame or RLE-compressed data there but it does not matter much as the main features are already discovered.

There are many various FLIC extensions, like high(er)-bitdepth video, custom RLE coding schemes and even audio support. And that’s not counting the fun things like FLIC-in-AVI or FLIC-in-AVI. But I leave documenting all those format variations to The Multimedia Mike, gaming and documenting FLIC are his passions.

As you can guess, my work on Real Video 4 encoder goes so well that I’d rather look at virtually anything else.

Probably some of you are aware of Tex Murphy game series (maybe not even just Mike) and I got reminded of an existence of The Pandora Directive game that supposedly has a lot of videos in it, so I downloaded a demo and decided to explore it a bit.

Game data is packed into extremely simple archive format (just the number of offsets and the offsets) so you need to know what archives to look into (hint: the larger ones).

So what about videos? They start with H2O magic (hence me calling it a watery format) and contain video frames and audio data (in an embedded WAV file). The video compression is both nothing special and somewhat original: it’s Huffman-compressed RLE. Video frame can contain several chunks, first there’s a Huffman tree description, then palette data and finally there’s compressed RLE data. The originality lies in the details: Huffman coding is often used to code single bytes while here single symbol represents both run length and value (also IIUC zero value signals skips), additionally the data is stored as the list of symbols for each codeword length. I don’t think I’ve seen anywhere neither RLE+Huffman used in such manner nor such tree description format.

This was a fun distraction even if I don’t care about the game series (I tried playing their other games like Countdown and Amazon: Guardians of Eden but the interface was too clunky and the action sequences were too annoying). It’s always nice to see some originality in video coding even if it is nothing advanced.

This is a resource format (as one could guess from its name) used by Beam Software for various resources in its games. The first time I had to deal with it was when some anonymous contributor contacted me with a REd decoder for videos in Lost Vikings 2. I adapted for FFmpeg (wow, it’s been fifteen years ago) and added sound support as well.

Recently I decided to revisit it (previously I tried to adapt decoder for 15-bit video but could not make it exactly right for some reason). So I looked at it, it turned out to be exactly the same algorithm but depending on whether palette is present in the frame (yes, 256-colour palette with RGB555 entries) pixel data is read either as byte palette indices or raw 16-bit values. I also looked at The Dame was Loaded game and its FCP format turned out to use exactly the same compression but with a different frame format (16-bit sizes, different audio/palette/video order and so on). And the game audio uses packed 12-bit PCM (two samples without low nibble are stored in three bytes) which is not something you often see.

And with that I’m done with game formats for a long time. Probably I should write a toy encoder or two now.

While the situation in Ukraine is stable bad so I keep looking at game formats instead of playing those games instead.

Apparently there’s a German adventure game from mid-1990s called Talisman and that’s about all I can tell about it. Yet it seems to have rather interesting animation format that’s worth talking about.

It turned out to be codebook-based compression with a codebook shared by a group of frames (typically 20-30) and actual codebook being created from a transmitted codebook data mixed with the static codebook (an interesting fact: unlike many other game formats, this one not merely allows seeking inside, there’s a special chunk preceding group of frames with the same codebook that contains an offset of the next such chunk). Tile operations are either copying 2×2 tile from another part of the frame (optionally updating one pixel in it) or reading it raw.

While it’s not the most complex format ever it turned out to be interesting enough. And with that I’ve probably exhausted the game video formats to look at. I’ll probably revisit SIFF but that’s about it.

While Iran wages a proxy war with Ukraine (and I can easily believe they’re not against doing it to the last russian), I’m still trying to distract myself by looking at various video formats in games I have no intention to play.

Finding games with unknown formats gets harder and harder (or at least more tedious). So here are two games with an interesting approach to video compression.

Dark Earth packs frames as separate planes with 5-bit components and each plane is compressed using a peculiar modification of LZ77 scheme: depending on a bit set, it either codes a run or a forward reference in either the same or previous buffer. Additionally it codes it using non-bytealigned stream (run mode is coded in 13 bits and copy mode takes 25 bits).

There’s also Defcon 5 game (the one from the mid-1990s, do not confuse it with a game with the same name but from a previous decade). This one employs a different method I don’t remember seeing anywhere else: painting squares. Of course you’re used to various codecs splitting tiles in blocks and filling them (from older codecs using quadtrees to H.26x and its rip-offs). This one does it differently though: there is a fixed set of tile sizes selected for each video (I’ve seen only 32, 16, 8, 4, 2 set though) and frame data is essentially a list of commands telling at which offsets to paint a tile of this size with a given colour (those offsets may be completely arbitrary). It may be not the most efficient compression algorithm but it’s quite interesting. Also the container specifies palette as fixed and changing colours—first part is stored in the header and the second part is transmitted with each frame. Again, it’s not something extremely effective but I can’t easily remember any other format doing it that way.

I’ll probably try to do something different next time but I consider time spent on looking at these formats well-wasted.