0xDEAFBEEF

Guide for Reconstructing Media

Summary: obtain the C source code and token's random hash value from Ethereum blockchain. Replace the 'seed' variable with this hash where indicated. Compile and run the program,obtaining the raw output (BMP and WAV files). Encode the raw output to MP4,MP3 using ffmpeg.

Step 1: Obtain the C source code file and your token's random hash value

Use a web3 client or etherscan.io to interact with the contract at https://etherscan.io/address/0xd754937672300ae6708a51229112de4017810934.

Use the getTokenParams() function, passing your token ID.

Note the 'seed' value which is the random hash that you will later need. 'codeLocation0' is the address of the transaction that contains the C source code. Visit that transaction address on etherscan, in this example it's https://etherscan.io/tx/0xf784123a3043f98fbdbb7efe168f61bf1d1f0eaea8fb46b5290abb3e759beae8 Press 'Click to see More' and view the 'Input Data' field as UTF-8.

Copy and paste the C source code into a file on your computer named main.c.

Step 2: Replace the 'seed' variable with token's unique random hash

Near the top of the C source file, there is a line:

char *seed="0x2c68ca657f166e1e7a5db2266ee1edca9daf2da5ecc689c39c1d8cfe0b9aad2e";

Replace that value with the 'seed' value previously read through getTokenParams().

Step 3: Install a C compiler for your platform.

Linux is the recommended platform, and GNU GCC is the recommended C compiler, available through default package managers. On Mac, you may be able to use Homebrew. On Windows, try GNU GCC binaries.

Step 4: Compile and run the program.

Code conforms to the ISO c99 standard. Only library dependency is C math library. Pass '-lm' to gcc. Assumes architecture is little endian (all Intel processors)

First, create directory to store output images:

$ mkdir 'frames'

Next, compile and run. Optionally pass '-Ofast' flag to enable optimization (faster rendering).

$ gcc -Ofast main.c -lm && ./a.out

This will produce:
a. Numbered image files in BMP file format stored in 'frames' directory. 24 FPS(frames per second)
b. Audio file named 'output.wav' in WAV format, stereo, 44.1khz, 16bit depth

This is the 'raw' information representing digital audio signals and image pixel intensities.

Step 5: Encode raw output to chosen media format(MP3, MP4, JPG, PNG, etc)

This raw information can be encoded perceptually using whatever tools exist at the time of reconstruction. At present, for example, opensource tools such as imagemagick and ffmpeg can be used to encode images,video and audio in different format for popular distributions. Linux platform is recommended, ffmpeg is available from default package manager. On Mac platform, use Homebrew to install ffmpeg.

Examples:

1. Audio can be encoded to MP3.
$ ffmpeg -i output.wav  -b 192k output.mp3

2. Images can be assembled into an animation and encoded to MP4, for example:
$ ffmpeg -framerate 24 -i frames/frame%04d.bmp -crf 20 video.mp4

3. audio can be encoded with video:
$ ffmpeg -i output.wav -i video.mp4 -c:v libx264 -c:a aac -b:a 192k -pix_fmt yuv420p  -shortest audiovisual.mp4

4. Screenshots of particular frames(in this example, frame 60), using imagemagick:
$ convert frames/frame0060.bmp -scale 720x720 image.png