Archive for the 'Tutorials' Category

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Adventures in Vector Quantization

Published on 01/08/2011 in Tutorials. 0 Comments Tags: , , , , , , , .

Ever since seeing Radio Dada by Rosa Menkman I’ve been forever trying to reproduce the style of compression/glitches it uses.

In my limited knowledge about the production of the video I do know what it uses compression artifacts found in the Cinepak codec. So, I set out to try and find a way of converting a video to a video that uses the Cinepak codec. If you’ve been following me you’ll that I’ve asked for help on many fora and mailing lists for help with initially little success.

Hidden somewhere in the documentation for MEncoder is a page detailing how to use Windows codecs on Linux for encoding. The copy of the Cinepak codec (iccvid.dll) that came with MEncoder/medibuntu was a bit broken so I had to use Google to download a new version.

Once I had that I used MEncoder to convert a video to an avi with the Cinepak codec. (I’m using mencoder version 2:1.0~svn33951~natty):

mencoder infile.avi -ovc vfw -xvfwopts codec=iccvid.dll -oac mp3lame -o outfile.avi

Unfortunately for me this did not produce the compression artifacts that I was after. I tried reencoding the video using the Cinepak codec several times but this only just made the video darker:


(Original video)

Also, my attempt to encode the video using the Cinepak codec but with a low bitrate didn’t work as, at least when using MEncoder, the codec doesn’t have any encoding options. Drats! With that said, if anyone knows of a way of encoding using Cinepak with low/different bitrates on Linux using only freely available/open source software please do let me/the world know.

After this I felt very disheartened until I did a little bit of digging into the actual codec. I discovered that this codec is one of a few is based on Vector Quantization. I don’t know much about this but I felt that this must be the key. The video codecs that are based on Vector Quantization are Sorenson, Indeo and VQA.

I had no luck finding a way of converting to Sorenson and Indeo. However, I’ve had more luck with VQA. Wikipedia has a bit of information on the codec:

Vector Quantized Animation, known by its acronym VQA is a file format originally developed by Westwood Studios for video encoding in their game The Legend of Kyrandia and monopoly.

If you ever came across a Sega Saturn you probably will have come across videos encoded using VQA. As that Wikipedia article states, apart from the one used by Westwood Studios, only one VQA encoder exists. VQA Encoder v0.5 beta 2 by ugordan is the only known VQA encoder and luckily it works perfectly using Wine (I’m using version 1.2.3-0ubuntu1~ppa1) on Ubuntu 11.04. You’ll have to download some additional DLLs. Just do some research to find out which ones.

In order to use the software you need to convert your video to image files. I’ve had luck with converting the video to PCX files using FFMPEG:

ffmpeg -i infile.avi -sameq outfile_%03d.pcx

Then, in the VQA Encoder v0.5 beta 2 copy these options:

VQA encoder options

The program will automatically recognise that there are many images in the folder. After encoding has finished you should have a file called out_.vqa. In FFMPEG execute:

ffmpeg -i out_.vqa -sameq outfile.avi

You should now have a video that has similar compression to the Cinepak codec used with low bitrates:


(Original video)

Brilliant! Well, not so brilliant. The problems with using this software are the following:

  • The software is no long being updated
  • Because of this it could stop working at any time and no support would be offered
  • It can only output video at 640×400, which you can see by the way it crops the video
  • It isn’t open source, though that only matters if you exclusively use open source software

So, is there any other way to achieve these compression artifacts, preferably using open source software?

What Glitch? scripts

Published on 11/03/2011 in Art and Tutorials. 5 Comments Tags: , , , , , .

For the What is Your Glitch? videos I wanted to build up on some of the extensive work that has already gone into the documentation, deconstruction and glitching of file formats. Rosa Menkman has already done a great job of documenting some of the more well-known file format glitches in the Vernacular of File Formats, which I recommend you all read. For this exercise I wanted to explore some of the more obscure file formats. Using open source software and Ubuntu has given me access to a wealth of programs that can still generate obscure file formats, such as pcx, pix and sgi. Through these experiments I also found inconsistencies in the way that different programs generate files, which is evident through my decision to use GIMP to convert files rather than Imagemagick in some of the scripts. Enough chit-chat, download the scripts!

Code hosted on GitHub

The method of glitching used in most of the scripts is the much-documented find and replace method. If you take a look in the scripts – and I encourage you to do so – you can change the characters that are being searched for and replaced. I’ve simply chosen characters that are sure to get results and are less likely to completely destroy the file.

Required Dependencies

Each script has its own set of dependencies, but to ensure you can run each one you’ll need the following:

  • Sed
  • GIMP – I use 2.71 beta available for Ubuntu from this ppa. Other versions remain untested
  • Imagemagick
  • GlitchSVG
  • FFMPEG
  • Mplayer
  • WebP

Basic Usage

1. Make the file executable: In a terminal type chmod+x [name of script] (e.g. what_glitch_webp.sh)
2. Run ./what_glitch_webp.sh in a terminal window
3. Drop a video file into terminal window and press Enter
4. Get a cup of tea

Notes

  • The scripts have only been tested on Ubuntu 10.10. If you are able to get them working with other operating systems please feel free to share your techniques
  • These scripts seem to work best with avi video files that are 24 or 25 frames per second. Files that are 30 frames per second get out of sync with the audio
  • Make sure the name of the directory containing the video to glitch doesn’t contain spaces e.g. “untitled_folder” instead of “untitled folder”
  • The video needs audio order for this script to work. If you know what you’re doing you can edit parts of this script for it to work on files that have no audio
  • As these scripts processes each frame of a video file it will take a very long time to complete. It is recommended for use only on small video clips!

These scripts by no means even begin to cover all of the image file formats available. There were a few formats that were not as easy to batch-process or were simply too large to process, such as xpm and xbm. For these you’ll have to do it manually or explore other ways of batch processing. They’re also not the most efficient of scripts. Some way into processing 400 video frames the script would slow down a lot. I welcome any bug fixes or suggestions on fixing this ;-)

There’s still plenty of undiscovered glitches out there in the wild just waiting to be hunted down and exploited. I encourage anyone, everyone and their mother to pick from this long, but by no means complete list of image file formats and to find a way to glitch them!

Create your own glitch typeface

Published on 16/07/2010 in Tutorials. 3 Comments Tags: , , , , , .

Making Dataface was really quite an exciting journey. What started off as an attempt to make a typeface inspired by glitch art turned out to be a story of collaboration, exploration and hours of research. Here, I will go through my process.

As you may have seen from my previous experiments in vector databending it’s totally possible to manipulate vector files. My original method for creating Dataface was to save each glyph in the Liberation font to an SVG file and then go through the process of glitching it for each file. Obviously this would’ve taken me a long time, hence why there was very little activity between my original announcement in January and when I started work on it again a few weeks ago.

At this time I thought about writing a script to do this for me. sed is a great command-line utility for Linux that essentially does the same as using find/replace on a character. As it’s command-line it means I can do a lot of automation with it. So, I wrote this simple script that attempted to solve the problem

#!/bin/bash
rand=$(($RANDOM % 9))
sed -i s/[0-9]/$rand/g fontfile.svg

The only problem was that it would replace all numbers in the file with whatever random value was chosen by $rand as the script was executed. Not only is this bad because it would result in a lot of strangely similar glyphs but also because it would modify the header data of the font file, thus rendering it unreadable. I soon remembered that recently the SVG Font specification was finished, which aided my cause by putting all of the glyphs in one big file, but I still couldn’t find a way to efficiently randomise values in the file.

Thankfully fizzPOP came to my rescue. I’m glad that hackerspaces have people with a range of abilities in hardware and software, as I was soon presented with a solution to my problem by GB. After a few revisions he created a script that would replace only specific values in the file and wold even let you specify how much it should be randomised. You can download the finished script and source files and have a go for yourself.

Click to download

 

Simplified instructions on compiling the script:

  • Unzip the file in a clean folder. This will give you three files:Font_Sample_-_Liberation_Sans.svg, glitch.l and makefile
  • Type “make” into the command line (without the quote)
  • If you haven’t got make, type: 
    flex -t glitch.l >glitch.c
    gcc -o glitch glitch.c

in either case, you will get a program called “glitch”.

Please note this has only been tested on Linux, requires Flex (available in the Ubuntu repository) and it is designed to work on SVG font files. I only know FontForge that is able to create these fonts files. To run the script do the following

./glitch 0.50 outputfile.svg

That tells the script to glitch the file by 50%. I have noticed that sometimes you get errors if you put in 1.00 or more.

Once you have generated the file you can import it back into FontForge to save as a .ttf, .otf or whatever font type you choose!

(I still hate Comic Sans)

Here’s everyone’s favourite Comic Sans glitched at 50%

Streams of data

Published on 01/02/2010 in Tutorials. 0 Comments Tags: , , , , , , , .

One of my overall goals is to find a way to databend live video. I’m sure there’s a way to do it with Processing and Pure:Data but I’m not yet proficient in those programs so they’re out of the question for now. In the meantime I thought to try and hack the Echobender script to databend my webcam images.

tonyg provides a great tutorial on how to convert live webcam images into audio, which I’ve used as a starting point for my hack.

The process for making it works is as follows:

  • Images from the webcam are saved to the computer
  • These are converted to a .bmp file then renamed to a .raw file
  • Sox applies an audio effect to the .raw file
  • The .raw file is converted back to a .bmp then to a .jpg
  • The updated webcam image is displayed to a window and updated once every second

Sound overly complicated? It probably is. Like the Echobender script you’ll need ImageMagick and Sox but we’ll also be using Webcam, which you can install via sudo apt-get install webcam

If you haven’t already, create a file called .webcamrc in your home directory (/home/yourusername) and enter this text into it:

[grab]
delay = 0
text = “”

[ftp]
local = 1
tmp = uploading.jpg
file = webcam.jpg
dir = .
debug = 1

Now create a file called grabframe, place it in your home directory and fill it with this:

#!/bin/sh

while [ ! -e webcam.jpg ]; do sleep 0.1; done
convert webcam.jpg frame.bmp
cp frame.bmp frame.raw
sox -r 482170 -e u-law frame.raw frame2.raw echos 0.8 0.9 5000 0.3 1800 0.25
convert -size 640x240 -depth 4 rgb:frame2.raw -trim -flip -flop output.bmp
convert output-0.bmp output.jpg

To start things running, open up three terminal instances:

  • In shell number one, run webcam.
  • In shell number two, run “while true; do ./grabframe ; done.
  • In shell number three, run display -update 1 output.jpg

Voila!

I know it’s quite slow, but I haven’t yet found a way to update faster and it’ll still be restricted by the time it takes Sox/ImageMagick to perform their conversions.

Thanks again to tonyg, Imbecil and Mez for their help and inspiration