Display anything on an Oscilloscope

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I've taken a few utilities and patched them together to convert any picture or movie to an audio file, which can be played on an oscilloscope in XY mode to display a vector drawing of the picture or video.

This is a demonstration of my oscilloscope playing the first few minutes of "Felix the Cat in April Maze" which is available at http://archive.org/details/Felix_AprilMaze_NoAudio

This video shows the weaknesses of my current method. The frame rate isn't constant and dependent on the total length of the lines in any given frame. Because of this it is very possible for the trace time to become so long the image starts to flicker, which happens in the scene where it's raining. The next thing I'll do is make the utility I've written repeat the same frame until a maximum number of samples have been created.

The oscilloscope was recorded with a Sony Vidicon camera and colourised with my JVC KM-3000 video effects processor. I'm using Linux to do the conversion (it will probably be more tricky in Windows)

The task is this:

• Convert the picture or movie to a PPM file, or array of PPM files (if it's a movie) with a resolution of 256x256 pixels. Mplayer can do this.
• Run Potrace on the PPM file/files to convert them to SVG files.
• With Inkscape installed, run "/usr/share/inkscape/extensions/hpgl_output.py" on the SVGs, outputting it to HPGL files.
• Render the HPGL file/files to raw audio. I've written a small utility to do this (see below). The output of it can be appended to the raw audio file.
• Convert the raw audio file to a WAV or FLAC at 96000Hz, 16-bits, little-endian and two channels with Audacity or SoX.

The quality of the vector image is very dependent on the sound card's bandwidth (both upper and lower cutoff frequencies).

Here is a Bash script that will do all of the above steps. You will also need to compile hpgl2wav.c to convert the plotter files to audio.