Post
Speedruns played back one frame at a time with save states, revealing what a theoretically perfect run looks like.
A TAS isn't played in real time. Runners use emulator features (frame advance, save states, rerecording) to craft an input file that plays back a perfect run. Every jump is pixel-perfect, every trick is frame-perfect, and RNG is fully manipulated. A single TAS can take months to produce, with thousands of rerecords per minute of gameplay. TASes aren't meant to compete with human runs; they exist to explore the absolute limits of a game and often discover new techniques that human runners later adopt.
Example
The TAS of Super Mario Bros. 3 completes the game in under 3 seconds using ACE to jump to the credits. Human runners can't replicate this, but TAS discoveries of individual tricks often filter down into real-time speedrun strategies.
Why it matters
TASes push game knowledge forward by finding tricks no human could stumble upon. They also create incredible entertainment: watching a TAS of a game you know well is like watching the game played by a god with infinite patience.
Related concepts