if you have 24Mb of memory and 250k samples/sec then it takes 100 seconds to fill the memory (more or less). That's 100 seconds between sweeps, 100 seconds between triggers.
I don't remember how low it goes, exactly, but it's a lower then 250k samples/sec.
You really wouldn't want to use full memory depth down there...
If you have 250k samples/sec don't even fantasise about looking at video signals.
An analog composite video signal at field rate has frequency components from 50Hz/60Hz up to around 5MHz, so at the above rate, you will just get a mess of aliased crap.
Your sampling rate has to be around 20M samples/second to get a useable display.
To fill a screen with one field of video, over a 20ms period requires 400k samples of memory.
This is why, when Tek & HP salesmen tried to sell early DSOs with tiny memories to TV Studios, they went away disappointed.
To make it even harder, we usually liked to display two fields.
Most of the old DSOs couldn't even cope at line rate!
The display on the linked video is really pretty poor----I'm sure I've seen better screenshots of video signals where the user had a DS1054Z.
Maybe it is the moving image---- the video component looks like it is continually drifting w.r.t. the syncs--- a most disturbing illusion!
On an analog 'scope, the signals stay synced, with the video signal just changing in amplitude & frequency
components.lo
PS. It just dawned on me what the problem with the linked video is.
It isn't a failing of the Oscilloscope, but rather, of the person producing the video.
They almost certainly didn't have a source of composite video, but
did have one for composite syncs & blanking.
They happily added a non- synched signal from a sig generator & "called it good"!
I
do remember seeing a very similar effect many years ago, when we were trying to check our BW Transmitters prior to colour mods, but didn't yet have any proper PAL generators.
We just added a 4.433MHz sine wave to a source of blanking & syncs, & the "video" drifted w.r.t. syncs in exactly the same way.