e8ac53f Oct 20, 2015
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asciicast file format (version 1)

asciicast file is JSON file containing meta-data like duration or title of the recording, and the actual content printed to terminal's stdout during recording.


Every asciicast includes the following set of attributes:

  • version - set to 1,
  • width - terminal width (number of columns),
  • height - terminal height (number of rows),
  • duration - total duration of asciicast as floating point number,
  • command - command that was recorded, as given via -c option to rec,
  • title - title of the asciicast, as given via -t option to rec,
  • env - map of environment variables useful for debugging playback problems,
  • stdout - array of "frames", see below.


Frame represents an event of printing new data to terminal's stdout. It is a 2 element array containing delay and data.

Delay is the number of seconds that elapsed since the previous frame (or since the beginning of the recording in case of the 1st frame) represented as a floating point number, with microsecond precision.

Data is a string containing the data that was printed to a terminal in a given frame. It has to be valid, UTF-8 encoded JSON string as described in JSON RFC section 2.5, with all non-printable Unicode codepoints encoded as \uXXXX.

For example, frame [5.4321, "foo\rbar\u0007..."] means there was 5 seconds of inactivity between previous printing and printing of foo\rbar\u0007....

Example asciicast

A very short asciicast may look like this:

  "version": 1,
  "width": 80,
  "height": 24,
  "duration": 1.515658,
  "command": "/bin/zsh",
  "title": "",
  "env": {
    "TERM": "xterm-256color",
    "SHELL": "/bin/zsh"
  "stdout": [
      "\u001b[1;31mHello \u001b[32mWorld!\u001b[0m\n"
      "I am \rThis is on the next line."