Developer Voices

Asciinema: Terminal Recording Done Right (with Marcin Kulik)

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Feb 19, 2026

Marcin Kulik, open-source creator of Asciinema and maintainer of its recorder, player, server, and Rust AVT emulator, joins to trace 14 years of rewrites. They cover terminal parsing and emulation, trade-offs in rendering and performance, moves from Python and ClojureScript to Rust/WASM, live streaming architecture, and how a single Rust emulator now powers multiple components.

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INSIGHT

Terminals Are State Machines

Terminal output is a stream of control sequences that must be parsed into a virtual screen buffer.
You cannot merely append bytes to a div; you need a terminal emulator to interpret cursor movement, colors and modes.

ADVICE

Replace Regex With A True Parser

Do build a proper ANSI/VT100 parser rather than ad-hoc regexes to avoid rendering bugs.
Use established state-machine references like Paul Williams' VT100 parser to guide implementation.

INSIGHT

Small Control Sequences Have Big Effects

Terminal behavior depends on many modes and subtle control-sequence termination rules.
Missing or unterminated control characters can cause text to be interpreted as control data instead of printable output.

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