BBC Four

Background
BBC Four was launched on 2 March 2002 as a replacement to BBC Knowledge (although it was planned to launch in 2001 and had plans dating back to 2000). BBC Four's programming consists of a similar focus to that of BBC Knowledge, and runs from 7PM to 4AM on the same stream as the CBeebies channel, although they are seperated on the electronic program guide.

1st ID (2 March 2002-10 September 2005)
Visuals: On a black background, there are CGI shapes, usually having purple or lights, that react to the music and the voice of the announcer. The BBC Four logo (a black box with the BBC logo at the top and "FOUR" in Gill Sans at the bottom) is seen in the bottom right corner.

Technique: CGI by Glassworks. This is rendered in real-time to the audio playing, both the music and the announcer.

Audio: Depends on the variant, though a continuity announcer is present.

Legacy: As this ident's animation was synced to the audio of the announcer and/or music, it stands out with the fact that no two idents were ever exactly the same.

2nd ID (10 September 2005-)
2005-2021=

Visuals: 4 different sections of the screen are shown, with the illusion that these are part of the same video. In the middle, the BBC Four logo can be seen. Several different idents have been made, one of the most famous being a "single" video of a lake with mountains in the distance, and ripples appear both in the lake's reflection and in the sky.

Later Variant: Beginning on 20 October 2021, with the introduction of the BBC's new logo, the idents were altered a bit. The square in the middle is gone, with the new BBC logo on top and the text "FOUR" in the BBC Reith font on the bottom, like the new BBC logo. The "Subtitles" graphic is now placed in a full widescreen picture, rather than being in its original place of a 4:3 picture.

Technique: Live-action with illusionary effects.

Audio: Depends on the variant, but there's a continuity announcer present. The main theme uses loud synth squeaks, and ends with a guitar note.

Availability: Current, being used for over 17 years as of October 2021, making it one of the longest-lived idents seen on British TV. It is currently unknown whenever the 4 sections could be replaced in the future.