THE RZX ARCHIVE: SPECTRUM VIDEO WALKTHROUGHS
ZX Spectrum emulation started almost as soon as the last Amstrad-built models had left the shelves in 1993, and in the next decade or two, just about every aspect of the original machines has been emulated. There are tape images, disc images, microdrive images, Interface 2 ROMs, memory snapshots, poke files, all of which relate to the original machine and its various peripherals. But one very interesting addition was the RZX file format, which recreates a series of accurately-timed keystrokes to make an perfect action replay, usually of a game being played, provided the initial tape or disc file is available. This is a vastly more efficient method of recording action replays compared to video. The RZX of Jet Set Willy II, which takes 67 minutes to play back, is only 413 KB; the equivalent 480p video is 153 MB, and at 720p this expands further to 480 MB. Admittedly a video file can be rewound or spun forwards, but for the size of the files, RZX is unbeatable.
Daren Pearcy hosts the RZX Archive, which collects all these RZX files together, usually with an accompanying YouTube video if the game is even remotely significant (obscure Czech text adventures or BASIC type-in games probably won't get one). Unsurprisingly, I've submitted a fair few myself, and equally unsurprisingly, I've usually had plenty of accompanying comments.
From most recent (2020) to furthest back in time (2003), this is my Ultimate Long List of RZX Archive contributions. In effect, it's my YouTube playlist run in reverse, but it also points to the relevant RZX Archive pages.
Also, all the screenshots from this page are from the RZX I submitted, they're not just random or pulled from Spectrum Computing or anywhere else.