which framerate to use?

[faust1103]

Hi,

I'm a newbie so please don't at me. I understand that vob files ripped have framerate of 25 fps (PAL) or 29.9xx (NTSC).

My question is:

If I want to encode such a file to DivX 5.02 do I leave the framerate the same as the respective source or do I have to change it to 23.97XXX? And if I have to change it why?
I had the impression that when I change the framerate the picture quality goes down. Also the GKont encoding log seemed to show an error regarding the totatl frame number.

Any help is welcome.

faust

[jggimi]

Start with this brief explanation:
--------
25 fps = PAL
29.97 fps = NTSC

24 fps = film. (That see-through stuff, with sproket holes on the sides. Processed chemically.)

"Telecine" = 24fps film converted to 29.97 for NTSC broadcast and/or DVD. Done by duplicating some frames.

IVTC = "Inverse Telecine" = A reducting in framerate from 29.97 to 23.976 fps. Done by removing those duplicate frames. "Force FILM" in dvd2avi is a simple type of IVTC, used for NTSC DVDs telecined from films.

(PAL encodings are not telecined. Just sped up 4%.)
--------

I don't work with PAL, my guess is I'd leave it at 25fps; read the guides if you want to try to change the framerate and adjust the audio accordingly.

For NTSC, your choices are: 1) Leave it at 29.97fps, 2) Force FILM, or 3) more robust IVTC.

For content that has not been telecined ... such as shot with a video camera ... I leave it at 29.97

For telecined content, so far Force FILM has worked well. The dvd2avi project file automatically adjusts the number of frames and the framerate.

Those who use more complex IVTCs should manually adjust the framerate within GKnot in order to correct the bitrate calculations.
+

[manono]

Hi-

If the source is PAL, it always stays at 25fps. If the source is NTSC, ordinarily the material was originally film at 23.976fps, so you Force FILM or IVTC to bring it back to it's original frame rate. But in some cases, the source was video, and you keep it at 29.97fps and just Deinterlace. These are difficult questions, and require lots of reading here and elsewhere to understand them.

But if you are going to work mainly with NTSC R1 Hollywood-type movies, you're pretty safe in just using Forced FILM.

Edit: jggimi types faster than I, and give more detailed answers. Do what he said.:)

[faust1103]

Thanks guys,

My head is really smoking now ;)

I understand now that it is smart to inverse telecine an NTSC framerate of 29.xx back to 23.xx.
But what's the diffrence between using Force Film (in DVD2AVI) or using IVTC (later in GK)? Is IVTC more "reliable" and therefore should be used with "pure" NTSC material?
Also if one uses IVTC is deinterlacing still needed (you can chosse one of the two in GK)?

Thanks again.

faust

[jggimi]

Force FILM is an automatic IVTC. The other methodologies are used for more complex content.

dvd2avi documentation sent me to this link. I can't say I understand it; it should be enough detail to keep your head smoking for days...

http://arbor.ee.ntu.edu.tw/~jackei/dvd2avi/ivtc/

[faust1103]

Ok,

I did a few more tests. I wanted to turn a ripped NTSC video clip (at 29.97 fps) into a Divx File (at 23.97 fps) using Divx 5.02 and GK.
DVD2AVI recognized the vob file as (pure) NTSC at 29.97 fps. when I chose Forced Film in DVD2AVI I got disturbing black lines (Interlacing ?) in the final .avi clip.

When I used IVTC later in GK (instead of Forced Film) the playback of the final divx file was a bit skippy (as if single frames were missing).
I am not sure what went wrong I set the framerate to 23.97 in GK and checked IVTC when creating the avs file.
I noticed that when I also checked IVTS frame correction at the last step (before you hit "add project to encoding que" I got an error message.

Could you guys tell me exactly which boxes I have to check in GK to downgrade an NTSC file to 23.97 fps? Thanks.

faust

PS: I also noted that if I left the framerate at 29.97 fps in the final divx file the video looked rather good (in fact better than at 23.97).

[jggimi]

Based on your last post, I can tell you're missing an important point:

You cannot use an inverse telecine process on content that was never telecined. If the original source WASN'T FILM, it won't have duplicate frames! IVTC removes duplicate frames -- which your source does not contain:....NTSC video clip.... (pure) NTSC at 29.97 fps...[list=1] A source shot with an NTSC video camera will need to stay at 29.97 fps. You've apparently missed instructions in GKnot and in Doom9's guide for previewing content with dvd2avi.[/list=1]Please read this sticky link in the dvd2avi forum, it describes the key words, like NTSC, FILM, PROGRESSIVE... what it means, and what to do about it:

http://forum.doom9.org/showthread.php?s=&threadid=23776

The vast majority of NTSC video camera source is interlaced. Your black lines are likely to be interlace artifacts.

[hakko504]

Originally posted by jggimi
(PAL encodings are not telecined. Just sped up 4%.)

This is not quite true. Most sources are sped up 4% but occasionally I have found some titles that has had extra frames added to them (1 in 24) in a kind of telecining.

[Dreassica]

This is not quite true. Most sources are sped up 4% but occasionally I have found some titles that has had extra frames added to them (1 in 24) in a kind of telecining.

that's true, DBZ PAL DVD's are one of those!!
They are a nightmare to encode

[jggimi]

Thank you for the correction. I meant to type "most" and didn't.
:stupid:

[Homo Elektrikus]

Is it a problem, not caring about film, ntsc, pal, hybrid etc, but simply putting donald graft's decomb -> telecide() in the avisynth script? You'll then have to use decimate to achieve deired framerate.

Greetz

[jggimi]

I don't know, having not used Telecide on progressive content. I'd think it would slow down your encoding jobs where it's not necessary.