Archive for the ‘Game Video’ Category

The original CfL codec

Thursday, August 17th, 2023

As most of you don’t know and don’t care, modern advanced video codecs may use the special prediction mode called “chroma from luma” where, as it’s obvious from the name, the chroma components are reconstructed from the luma using some coefficients. And what do you know, I’ve found a codec that used this approach back in 1997.

So there’s a French company called Kalisto Entertainment and back in the day it developed a codec for the cutscenes in some of its games (at least Dark Earth and Nightmare Creatures). 15-bit RGB video is split into three components and each is coded separately using simple LZ77-like method (i.e. it’s either RLE mode, or copy with an offset from the current or previous frame). The twist comes from the fact that those components are split into tiles (usually 20×20 ones) and each tile has coding mode and two sets of scale/offset coefficients, so for each tile one of RGB components is selected as the base one and two others are coded as the differences from the scaled (and offset) base value.

So one component plane contains the base components for each tile (which may be different for each tile) and the other two contain the differences for the predicted non-base components (which, at least in theory, should be mostly zeroes and thus better compressible). So when some people wonder if it’s time for video codecs to perform optimal component decorrelation on per-frame basis, here’s a practical codec from the last century that did it per-tile.

Looking at Digital Pictures video format(s)

Monday, June 26th, 2023

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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Looking at even more game formats

Friday, June 23rd, 2023

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.

Looking at yet another weird game format

Wednesday, June 21st, 2023

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).

Conquering yet another game format

Sunday, June 18th, 2023

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.

A quick look at a watery game video format

Monday, April 24th, 2023

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.

Looking at KQ6 Mac videos

Friday, November 25th, 2022

The terrorist country proves that it is recognized as one and keeps targeting civilians instead of fighting a war. So nothing new but it would still be nice to see its demise soon. Meanwhile I keep doing small things to distract myself from all this.

Since I have nothing better to do, I watch reviews of various games including the ones I know well. And one of those reviews mentioned that Macintosh version of King’s Quest VI: Heir Today Gone Tomorrow had peculiar intro. Actually every version of the game has something peculiar about its intro: DOS version uses Sierra’s own RLE-based SEQ format, Windows version uses standard MS Video 1 in AVI (it was my first sample with palette change messages), Amiga version is a reimplementation by Revolution Software on their Virtual Theatre engine altogether (maybe ScummVM will support it one day for all three and a half fans waiting for that). So, what’s with Macintosh version?

First of all, the files are QuickTime movies in the original Macintosh format where frame data is stored in the data fork and movie header is stored inside the resource fork. Since not all modern OSes support such files natively (or conveniently), I’ve hacked a support for such movies in MacBinary format that keeps all forks in one file. And what do we have inside?

Inside the files are video streams packed with Cinepak. One of the peculiarities is that they have palette specified in video header in the format different from the conventional MOV color atom format, let alone the fact it should not be present at all. I understand that for Cinepak and even more for Indeo 3 (I really should write an encoder for it one day) it was common to provide a palette so they rendered their output for 256-colour mode but in that mode Cinepak simply coded palette indices and here we have YUV420 output and a palette as a recommendation.

Then there’s a fun case with tracks in KQ6Movie. I understand that they split video and coded it in several tracks so they could use different palettes (and framerates as it turns out) for different segments. And those tracks are not in order. Tracks 0 and 1 seem to be the very beginning, track 2 corresponds to a scene somewhere in the middle and track 3 is the last intro scene. Other ten tracks are not in order either. Maybe there is some information hidden in the header telling the order but I’m too lazy to find it out (let alone implement).

All in all, this was unexpectedly weird.

A final look at SIFF

Saturday, October 29th, 2022

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.

Looking at Talisman animations

Thursday, October 27th, 2022

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.

A quick look at PDQ2

Friday, October 21st, 2022

So there’s this new service discmaster.textfiles.com for searching for files from some old disks and discs at archive.org and out of curiosity I took a look at what it offers.

While it’s physically impossible to check all hundreds of millions of files it indexes (even just videos), I took a look at one rather curious category called aviAudio. There are about six hundred files of such type found so I decided to check them to see what kind of beast that is.

Some files turned out to exactly AVI audio files—AVI files with single stream that turns out to be audio (I don’t know why but this happens). The rest of the files were AVIs with unrecognized video track (just what I was hoping for!). One set of the samples come from some game with IPMA codec, other sources mostly feature Motion Pixels video (which is horrible both to RE and to support so I’d rather not touch it), one sample was special “codec” for some russian erotic game (which means complete garbage even by russian game standards) that is really just obfuscated Indeo 5. And finally there was a single PDQ2 sample (from some Incredible Hulk game demo from 1997).

An interesting thing is that it’s a DOS game with built-in AVI demuxing and decoding of this codec. The codec turned out to be a lot like various lossless codecs (so its FOURCC probably stands for something like “pretty damn quick codec, version 2”). It splits video into 4×4 tiles and emits up to three streams stored one after another: tile opcode (copy previous tile, copy previous data with an arbitrary offset, skip tile, raw tile), variable offsets and tile pixels. Additionally frame data may be packed further with LZ77-based scheme. As I said, a rather familiar scheme for lossless video codecs and it makes me wonder whether it’s a codec developed specifically for the game(s) or it was borrowed from somewhere else.