Question about VHS vs DVD when paused

[Jskid]

Back in the day when a VHS was paused (or fastforwarded or rewound) the image would shake and there would be horizontal lines across the screen. How come DVD players don't have that problem? If you pause a DVD the picture is perfectly still?

 

[Lokalaskurar]

Mainly because the DVD-player works by buffering the video-imaging into a RAM, which then is read when playing the video.

A VHS-still works by halting the tape and continuously reading a requested frame (of maybe 1 ms), which is edged magnetically into the tape. In other words; the head reading the tape has to read that 1ms (it's certainly more than just 1 ms BTW.) over and over and over again until you unpause. Thus the head renders the data read from the tape as it reads just a slight portion continuously => creating a shaking effect = the same frame rendered over and over again.

A DVD-still on the other hand works completely different, as it works by buffering the video-imaging into a RAM, which then is read when playing video. This buffering of data is halted when you press "still", and the data portion rendered into the RAM is being displayed the same way a PC displays an image: simply not changing the pixels from their altered state.

That's the gist of it, at least

 

[Benny26]

@ Lokalakurar

Kudos for your explination but i think a "because DVDs are better quality and not 30 years old" would have been enough

 

[Lokalaskurar]

Oh, that's only the gist of it

 

[mike1959]

Also Video recorders for the home market were built down to a very low price, one of the main problems was that each tape had to capable of storing at least 2.5 hours of tv program, which in turn meant the tape had to pass very slowly over the head, so the quality was not very high. (even with the head spinning). Tape Video recorders could be high quality, as proved by BBC and all tv production companies, but they used U-Matic system, far better, but also very expensive, too expensive for the home market.

 

[yRaz]

Mainly because the DVD-player works by buffering the video-imaging into a RAM, which then is read when playing the video.

A VHS-still works by halting the tape and continuously reading a requested frame (of maybe 1 ms), which is edged magnetically into the tape. In other words; the head reading the tape has to read that 1ms (it's certainly more than just 1 ms BTW.) over and over and over again until you unpause. Thus the head renders the data read from the tape as it reads just a slight portion continuously => creating a shaking effect = the same frame rendered over and over again.

A DVD-still on the other hand works completely different, as it works by buffering the video-imaging into a RAM, which then is read when playing video. This buffering of data is halted when you press "still", and the data portion rendered into the RAM is being displayed the same way a PC displays an image: simply not changing the pixels from their altered state.

That's the gist of it, at least

that was really interesting, thanks for the good read.