Glitch News

News photos, mostly from Japanese sources, as they might be interpreted by a malfunctioning JPEG renderer. Above: The Fukushima Daiichi nuclear power plant.

Did you know you can put (almost) arbitrary data into a WAV file’s PCM stream? It’s true, and the results sound as mechanical and unlistenable as you might expect. In the spirit of the old Everything2 node “catting weird things to /dev/audio”, here’s how I created this:

$ curl -s https://raw.github.com/knu/ruby-unf_ext/master/ext/unf_ext/unf/table.hh | \
  ffmpeg -codec:a pcm_s16le -f s16le -ac 2 -i - -f wav output.wav

A breakdown of the above FFmpeg invocation:

• -codec:a specifies the audio codec I want to use to decode the input data. Here, we’re pretending the C++ header file I fetch using curl is actually signed 16-bit little-endian PCM audio data. You may also know this option as -acodec.

• -f s16le specifies the input file format, which in this case is basically the same as the audio codec. This is necessary to make FFmpeg understand that we’re providing it with raw data, and not expect file headers or metadata or what have you.

• -ac 2 tells FFmpeg to treat the input as having two audio channels, in essence stereo audio. You can leave this off and get mono audio; with the same data, it sounds like it’s being played at half-speed.

• -i - means that the data is coming from standard input.

• -f wav specifies the output file format. You might be thinking, “Wait, didn’t you already use -f?” Indeed I did. Options that come before -i generally apply to the input stream, while options after it apply to the output stream. Intuitive, huh?

As is my usual admonition, don’t do this.