Breaking Eggs And Making Omelettes

Topics On Multimedia Technology and Reverse Engineering


Subtitling Sierra VMD Files

May 31st, 2016 by Multimedia Mike

I was contacted by a game translation hobbyist from Spain (henceforth known as The Translator). He had set his sights on Sierra’s 7-CD Phantasmagoria. This mammoth game was driven by a lot of FMV files and animations that have speech. These require language translation in the form of video subtitling. He’s lucky that he found possibly the one person on the whole internet who has just the right combination of skill, time, and interest to pull this off. And why would I care about helping? I guess I share a certain camaraderie with game hackers. Don’t act so surprised. You know what kind of stuff I like to work on.

The FMV format used in this game is VMD, which makes an appearance in numerous Sierra titles. FFmpeg already supports decoding this format. FFmpeg also supports subtitling video. So, ideally, all that’s necessary to support this goal is to add a muxer for the VMD format which can encode raw video and audio, which the format supports. Implement video compression as extra credit.

The pipeline that I envisioned looks like this:

VMD Subtitling Process

VMD Subtitling Process

“Trivial!” I surmised. I just never learn, do I?

The Plan
So here’s my initial pitch, outlining the work I estimated that I would need to do towards the stated goal:

  1. Create a new file muxer that produces a syntactically valid VMD file with bogus video and audio data. Make sure it works with both FFmpeg’s playback system as well as the proper Phantasmagoria engine.
  2. Create a new video encoder that essentially operates in pass-through mode while correctly building a palette.
  3. Create a new basic encoder for the video frames.

A big unknown for me was exactly how subtitle handling operates in FFmpeg. Thanks to this project, I now know. I was concerned because I was pretty sure that font rendering entails anti-aliasing which bodes poorly for keeping the palette count under 256 unique colors.

Computer Science Puzzle
When pondering how to process the palette, I was excited for the opportunity to exercise actual computer science. FFmpeg converts frames from paletted frames to full RGB frames. Then it needs to convert them back to paletted frames. I had a vague recollection of solving this problem once before when I was experimenting with a new paletted video codec. I seem to recall that I did the palette conversion in a very naive manner. I just used a static 256-element array and processed each RGB pixel of the frame, seeing if the value already occurred in the table (O(n) lookup) and adding it otherwise.
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Posted in Game Hacking | 8 Comments »

Running Windows XP In 2016

January 1st, 2016 by Multimedia Mike

I have an interest in getting a 32-bit Windows XP machine up and running. I have a really good yet slightly dated and discarded computer that seemed like a good candidate for dedicating to this task. So the question is: Can Windows XP still be installed from scratch on a computer, activated, and used in 2016? I wasn’t quite sure since I have heard stories about how Microsoft has formally ended support for Windows XP as of the first half of 2014 and I wasn’t entirely sure what that meant.

Spoiler: It’s still possible to install and activate Windows XP as of the writing of this post. It’s also possible to download and install all the updates published up until support ended.

The Candidate Computer
This computer was assembled either in late 2008 or early 2009. It was a beast at the time.

New old Windows XP computer
Click for a larger image

It was built around the newly-released NVIDIA GTX 280 video card. The case is a Thermaltake DH-101, which is a home theater PC thing. The motherboard is an Asus P5N32-SLI Premium with a Core 2 Duo X6800 2.93 GHz CPU on board. 2 GB of RAM and a 1.5 TB hard drive are also present.

The original owner handed it off to me because their family didn’t have much use for it anymore (too many other machines in the house). Plus it was really, obnoxiously loud. The noisy culprit was the stock blue fan that came packaged with the Intel processor (seen in the photo) whining at around 65 dB. I replaced the fan and brought the noise level way down.

As for connectivity, the motherboard has dual gigabit NICs (of 2 different chipsets for some reason) and onboard wireless 802.11g. I couldn’t make the latter work and this project was taking place a significant distance from my wired network. Instead, I connected a USB 802.11ac dongle and antenna which is advertised to work in both Windows XP and Linux. It works great under Windows XP. Meanwhile, making the adapter work under Linux provided a retro-computing adventure in which I had to modify C code to make the driver work.

So, score 1 for Windows XP over Linux here.

The Simple Joy of Retro-computing
One thing you have to watch out for when you get into retro-computing is fighting the urge to rant about the good old days of computing. Most long-time computer users have a good understanding of the frustration that computers keep getting faster by orders of magnitude and yet using them somehow feels slower and slower over successive software generations.
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Posted in General | 15 Comments »

Things I Have Learned About Emscripten

August 31st, 2015 by Multimedia Mike

3 years ago, I released my Game Music Appreciation project, a website with a ludicrously uninspired title which allowed users a relatively frictionless method to experience a range of specialized music files related to old video games. However, the site required use of a special Chrome plugin. Ever since that initial release, my #1 most requested feature has been for a pure JavaScript version of the music player.

“Impossible!” I exclaimed. “There’s no way JS could ever run fast enough to run these CPU emulators and audio synthesizers in real time, and allow for the visualization that I demand!” Well, I’m pleased to report that I have proved me wrong. I recently quietly launched a new site with what I hope is a catchier title, meant to evoke a cloud-based retro-music-as-a-service product: Cirrus Retro. Right now, it’s basically the same as the old site, but without the wonky Chrome-specific technology.

Along the way, I’ve learned a few things about using Emscripten that I thought might be useful to share with other people who wish to embark on a similar journey. This is geared more towards someone who has a stronger low-level background (such as C/C++) vs. high-level (like JavaScript).

General Goals
Do you want to cross-compile an entire desktop application, one that relies on an extensive GUI toolkit? That might be difficult (though I believe there is a path for porting qt code directly with Emscripten). Your better wager might be to abstract out the core logic and processes of the program and then create a new web UI to access them.

Do you want to compile a game that basically just paints stuff to a 2D canvas? You’re in luck! Emscripten has a porting path for SDL. Make a version of your C/C++ software that targets SDL (generally not a tall order) and then compile that with Emscripten.

Do you just want to cross-compile some functionality that lives in a library? That’s what I’ve done with the Cirrus Retro project. For this, plan to compile the library into a JS file that exports some public functions that other, higher-level, native JS (i.e., JS written by a human and not a computer) will invoke.

Memory Levels
When porting C/C++ software to JavaScript using Emscripten, you have to think on 2 different levels. Or perhaps you need to force JavaScript into a low level C lens, especially if you want to write native JS code that will interact with Emscripten-compiled code. This often means somehow allocating chunks of memory via JS and passing them to the Emscripten-compiled functions. And you wouldn’t believe the type of gymnastics you need to execute to get native JS and Emscripten-compiled JS to cooperate.
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Posted in Cirrus Retro | 5 Comments »

Emscripten and Web Audio API

April 28th, 2015 by Multimedia Mike

Ha! They said it couldn’t be done! Well, to be fair, I said it couldn’t be done. Or maybe that I just didn’t have any plans to do it. But I did it– I used Emscripten to cross-compile a CPU-intensive C/C++ codebase (Game Music Emu) to JavaScript. Then I leveraged the Web Audio API to output audio and visualize the audio using an HTML5 canvas.

Want to see it in action? Here’s a demonstration. Perhaps I will be able to expand the reach of my Game Music site when I can drop the odd Native Client plugin. This JS-based player works great on Chrome, Firefox, and Safari across desktop operating systems.

But this endeavor was not without its challenges.

Programmatically Generating Audio
First, I needed to figure out the proper method for procedurally generating audio and making it available to output. Generally, there are 2 approaches for audio output:

  1. Sit in a loop and generate audio, writing it out via a blocking audio call
  2. Implement a callback that the audio system can invoke in order to generate more audio when needed

Option #1 is not a good idea for an event-driven language like JavaScript. So I hunted through the rather flexible Web Audio API for a method that allowed something like approach #2. Callbacks are everywhere, after all.

I eventually found what I was looking for with the ScriptProcessorNode. It seems to be intended to apply post-processing effects to audio streams. A program registers a callback which is passed configurable chunks of audio for processing. I subverted this by simply overwriting the input buffers with the audio generated by the Emscripten-compiled library.

The ScriptProcessorNode interface is fairly well documented and works across multiple browsers. However, it is already marked as deprecated:

Note: As of the August 29 2014 Web Audio API spec publication, this feature has been marked as deprecated, and is soon to be replaced by Audio Workers.

Despite being marked as deprecated for 8 months as of this writing, there exists no appreciable amount of documentation for the successor API, these so-called Audio Workers.

Vive la web standards!

Visualize This
The next problem was visualization. The Web Audio API provides the AnalyzerNode API for accessing both time and frequency domain data from a running audio stream (and fetching the data as both unsigned bytes or floating-point numbers, depending on what the application needs). This is a pretty neat idea. I just wish I could make the API work. The simple demos I could find worked well enough. But when I wired up a prototype to fetch and visualize the time-domain wave, all I got were center-point samples (an array of values that were all 128).

Even if the API did work, I’m not sure if it would have been that useful. Per my reading of the AnalyserNode API, it only returns data as a single channel. Why would I want that? My application supports audio with 2 channels. I want 2 channels of data for visualization.

How To Synchronize
So I rolled my own visualization solution by maintaining a circular buffer of audio when samples were being generated. Then, requestAnimationFrame() provided the rendering callbacks. The next problem was audio-visual sync. But that certainly is not unique to this situation– maintaining proper A/V sync is a perennial puzzle in real-time multimedia programming. I was able to glean enough timing information from the environment to achieve reasonable A/V sync (verify for yourself).

The next problem I encountered with the Web Audio API was pause/resume facilities, or the lack thereof. For all its bells and whistles, the API’s omission of such facilities seems most unusual, as if the design philosophy was, “Once the user starts playing audio, they will never, ever have cause to pause the audio.”

Then again, I must understand that mine is not a use case that the design committee considered and I’m subverting the API in ways the designers didn’t intend. Typical use cases for this API seem to include such workloads as:

  • Downloading, decoding, and playing back a compressed audio stream via the network, applying effects, and visualizing the result
  • Accessing microphone input, applying effects, visualizing, encoding and sending the data across the network
  • Firing sound effects in a gaming application
  • MIDI playback via JavaScript (this honestly amazes me)

What they did not seem to have in mind was what I am trying to do– synthesize audio in real time.

I implemented pause/resume in a sub-par manner: pausing has the effect of generating 0 values when the ScriptProcessorNode callback is invoked, while also canceling any animation callbacks. Thus, audio output is technically still occurring, it’s just that the audio is pure silence. It’s not a great solution because CPU is still being used.

Future Work
I have a lot more player libraries to port to this new system. But I think I have a good framework set up.

Posted in HTML5 | 3 Comments »

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