What is the difference between the 3 framerate choices for MPEG DVD? CS4

J

joshtownsend

Well-known member
Tell me the difference between a DVD that is made with each of the 3 setting. 23.976, 29.97 drop frame, 29.97.

Here's my take. I tried the Adobe forums but not a soul can figure it out.

23.976 - records a 23.976 stream giving more space for a better encode. Has flags telling the dvd player what fields to duplicate to so you seeing 23.976p.

29.97 with drop code - records a 29.97 stream, giving giving the player flags that tell it what's fields to take away so your seeing 23.976p.

29.97 non-dropframe - records a 29.97 stream and that's what you see
 
maybe its something like this:

23.976 - 24p to 24i for a TV or other interlaced display
29.97 drop - 30p to interlaced footage for broadcast on SD TV
29.97 non drop - for 29.97 footage that is already 29.97

any reason this wouldn't be the case?
 
23.976 is for a 24p DVD. It will have the flags for a DVD player to insert pulldown for a standard TV. (There is no 24i.)

The 29.97 options will give you the same video; only the timecode will change, and it's a numbering thing only -- they have the exact same number of frames. No frame is actually dropped; it's only a number from the timecode sequence dropped periodically.
 
David, I've tried explaining this to people and when ever I qualify it this phrase "DVD player to insert pulldown for a standard TV" just confuses the hell out of people. Is there a better way to describe it?

'insert a pulldown' to 23.976 footage just doesn't sound right because you could also say that the 29.97 drop-frame preset 'inserts a pulldown'.

Also I'm right in saying Encore will not make a 24p DVD (I know it does this for blu-ray's). The 29.97 frame rate is not changable when making a SD DVD.
 
But that's exactly what it's doing -- the DVD player is inserting pulldown. 24p footage in a 29.97 file already has pulldown inserted; the DVD player doesn't do anything but read the file straight.

The difference is that with a 24p DVD, only the flags are in the file on the DVD -- that is, only the instructions. No extra fields are inserted in the file; it's a 24p file. The player then reads the instructions and inserts the extra fields where needed to make the 24p stream into a 29.97 stream.

Truthfully, it's actually not something you can explain in single sentence and make it crystal clear; you need a little bit of a grounding in how 24p works, especially vis-a-vis the NTSC TV standard, before you can really understand what a DVD player is doing.

About Encore -- you're saying there's no option to change the frame rate; I assume you say that because the frame rate is greyed out. But remember -- a single DVD can hold files of multiple frame rates. Most Hollywood DVDs have the feature portion in a 24p stream and all the extra material in a 29.97 stream, all on the same DVD. You don't define a DVD as a 24p or 29.97 DVD at the project level -- the frame rate is whatever the file on the disc is. If you feed Encore a 24p file, you can put on disc that way.
 
"The difference is that with a 24p DVD, only the flags are in the file on the DVD -- that is, only the instructions. No extra fields are inserted in the file; it's a 24p file. The player then reads the instructions and inserts the extra fields where needed to make the 24p stream into a 29.97 stream."

When I export the clip using all 3 presets (CBR DVD mpeg2) the file sizes are the same. Also if 29.97-with-dropframe gives you the same output and 24p cadence what is the point of 23.976?

Thanks Jim.
 
josh townsend said:
When I export the clip using all 3 presets (CBR DVD mpeg2) the file sizes are the same.
Click to expand...

This, I can't explain without more research, though using CBR isn't necessary and in fact is not the most efficient way to go.


Also if 29.97-with-dropframe gives you the same output and 24p cadence what is the point of 23.976?
Click to expand...

A pure progressive file will not display interlace artifacts on a progressive screen (when played by a progressive-scan player). If it's being played to a standard TV only, and the files end up being the same size, then there's not necessarily any advantage -- but the file sizes shouldn't be the same and I'll have to look into it when I get a chance.
 
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