Frame Rate When Ripping DVDs?

[Bobby Hall]

Thanks Dave and Nick!

I thought DVDs were interlaced (480i) and don’t store progressive files. Is this not true? Is there really a 24p file on the DVD (I’m using whole numbers for the sake of simplicity) or is it really 48 interlaced fields with flags to do 2-3 pull down? If there really is a progressive file on there, why aren’t DVDs called 480p instead of 480i?

And when I’m ripping DVDs in MPEG Streamclip, should I uncheck “interlaced scaling”? And what about the “deinterlace” option?

[Nick Meyers]

they are interlaced

“should I uncheck “interlaced scaling”?”
i dont know , what does the manual say

no don’t de-interlace. you need the fields for the pulldown to work.

basically rip from the DVD as clean as possible, do everything else afterwards.
that’s what i would do.

[Bobby Hall]

Dave, when I asked if a 24fps film on a DVD is really 24 frames or 48 interlaced fields, I was using the term “interlaced” to mean progressive segmented frames (never heard that term till you used it). I understand that the two fields of a progressive frame represent the same instance in time. So what I meant to ask was, is the file on the DVD 24fps, or is it actually 48 segmented frames per second? If the file is 24 fps, then wouldn’t that mean the DVD has flags that tell the player to split up those frames into segmented frames (two fields per frame representing no change in time), and then displaying those 48 segmented frames using 2-3 pulldown?

Also, if I have a DVD of a tv show that was shot with video, this means it was shot 60 fields per second, right? And when put on a DVD, it combines those fields into 30 fps. So in this case, the two fields of a frame are different instances of time. So wouldn’t this make each frame blurrier than a 24p frame? If you pause a 24p file, you’re seeing an entire frame of a still moment in time. And when you pause a 30i frame, you’re seeing two interlaced fields recorded 1/60 of a second apart, right?

[Bobby Hall]

Thanks for all the info. I was curious, why are DVDs encoded with the 29.97 frame rate instead of the field rate? If digital video is recorded at 59.94 fields per second and also shown on analog TVs at 59.94 fields per second, what’s the point in taking an extra step and encoding them to a frame rate if they’re just going to be displayed as a field rate later on? When movies first started to be edited digitally, was there some type of requirement that 24 fps movies had to be converted to 29.97 for editing?

[Bobby Hall]

Since progressive TVs show progressive frames and a film movie from a progressive DVD player will be shown at 24fps, that got me wondering about how DVDs are displayed with other types of players and TVs used.

Regarding a 24fps movie DVD:

Will playing that movie on an interlaced DVD player on an analog TV show the movie at 30 fps (60 fields per second)?

How many fps will the movie be displayed at with an interlaced DVD player on a progressive TV? Will the TV remove the repeated fields and display 24 fps?

Obviously using a progressive player and progressive TV will display at 24 fps, but what about a progressive player with an analog (interlaced) display? Will it show 24 fps or use the 2-3 pulldown flags and display at 30 fps? And if it’s 30 fps, is it showing complete frames or is it actually 60 segmented frames per second (showing the odd lines of one frame for 1/60 of a second and then the even lines of the same frame for 1/60 of a second)?

[Michael Gissing]

The speed difference is .1%, far too small to have any pitch consequences.

My understanding of the need to shift frame rates from 30 to 29.97 was that the color subcarrier was being modulated by the line frequency of 60hz causing a moire pattern on B&W TVs. Rather than solve this issue, NTSC just changed the frame rate of color broadcasting, thereby creating a nightmare for everyone who came after them.

Sometimes an engineers elegant solution has longer term tragic consequences, much like the decision to have two toally different shaped CO2 filters on the Apollo mission.