Help with understanding when to change frame rate

[mlaran]

Hi

I need some guidance on Frame rates. here is my question -- If I have a file with a specific frame rate should I convert it to DVD or to another type of file (example MP4 to AVI or MKV to AVI), should i always keep the frame rate constant with the source file? It looks like convertX to DVD automatically goes to 30 fps (for NTSC, which is what I need) and some of my sorce files are 24 or 25 fps. DVDFAB also has me select the frame rate and I always just put in 29.97 fps. Not really sure what to do.

I started wondering about this because I noticed that my standalone dvd / div X player (made by philips) seems to playback some files very jittery - even though the video / audio sync is good. So I thought it may have to do with frame rates which I should be converting.

Any info on understanding when I should and shold not be changing frame rates would be very helpful. I searched everywhere and found a lot of information on how to change the frame rate but none on when or why a frame rate should be changed

Thanks in advance

[jagabo]

NTSC DVD only supports one frame rate: 29.97 fps. That can be 29.97 interlaced frames or anywhere from 20 to 30 fps progressive frames with pulldown flags or hard telecined into 29.97 fps interlaced. The best way to get 20 to 30 progressive fps sources into DVD compatibility is to encode at the native frame rate as progressive MPEG 2 then add pulldown flags with DgPulldown.

[mlaran]

jagabo -- thank you so much you are awesome -- so when I convert froom let's say an mkv file with 24 fps should I convert that to 29.97 or leave at the original frame rate. Does chnging the frame rate cause jittery results??

[jagabo]

A 24 fps (probably really 23.976 fps) mkv should be encoded to 24 fps progressive MPEG2 and 3:2 pulldown flags added for the DVD player. Most MPEG encoders for DVD can do this. Most commercial DVDs are made this way.

24 fps films are inherently jerky. Watch any sharp, high contrast, medium speed, smooth panning shot at a theater and the jerkiness is obvious. When displayed on an NTSC TV it has 3:2 pulldown judder as well as the jerkiness of film. But that's the best you can do. If your computer can play a 60 fps Xvid AVI smoothly see the sample clip in this post:

https://forum.videohelp.com/threads/307004-Best-framerate-conversion-%28eg-23-97-to-30-...=1#post1888926

What you may be seeing with a Divx/DVD player is the conversion of frame rates by duplicating frames. For example you can convert 25 fps to 30 fps by duplicating every 5th frame. But those duplicate frames cause the video to jerk 5 times a second.