Terminal recordings

An asciinema recording (asciicast v2 or v3) is an image whose file ends in .cast:

![cast](demo.cast)
![The failing build](demo.cast#t=12.5)

Syntax

The file is read from the deck’s folder: a URL, an absolute path or a path that leaves the folder is refused. The alternative text names the recording for screen readers; cast alone means the recording’s own title. #t=12.5, or #t=1:23 for minutes and seconds, picks the moment that the outputs which cannot move show; without it, that is the end of the recording.

What each output shows

• HTML (the page, and the playground’s preview): the recording replays in a small player of go-slides, embedded in the page: play and pause, a speed button and a position bar. It loads no script from anywhere and uses no network.
• PDF, PowerPoint and OpenDocument (--pdf, --pptx, --odp): the terminal at the moment #t= names, as vector text in the theme’s monospace font, with the 16, 256 and direct colours, bold, italic, underline and inverse text. The text can be selected and searched. It is never a picture. Bold and italic are drawn where the theme’s monospace font has them (Roboto Mono in the gaia theme).

The player

It plays once, the first time the recording is on screen. When the browser asks for less motion (prefers-reduced-motion), it starts paused, showing the moment #t= names, and plays when you press play. Its buttons and keys do not turn the slide.

Limits

A recording is untrusted input, so it is bounded: the file (16 MiB), the events (500,000), the length (3 hours), the terminal (400 by 200 cells) and the work the emulator may do. A recording over a bound, or not a well formed asciicast file, is refused: the build goes on, the slide shows a note in its place, and the problem is a warning with a code: cast.syntax, cast.limit, cast.version or cast.path.

In the playground

Add a .cast file to the project from the Files panel, by dropping it or from the file picker. It goes into media/ and is inserted as an image. It is text that the deck reads, so it counts with the project’s other text files, which are limited to 2 MiB. Try it in the playground.