Telecine, Interlace, Progressive -> De-Interlace?

[flobbo]

Hello All!

I have just entered the world of cvd and svcd encoding a while ago and I am really confused with the above terms. I have browsed the forum for information and it seems everybody says something different. If I am encoding cvd or svcd do I need to deinterlace at all? How do I inverse telecine? Is it necessary? How do I find out what my source DVD is? Are there progressive dvds or is it all interlaced? Is there a difference between PAL and NTSC dvds when it comes to interlacing? Please help me out here. Thanks.

[flobbo]

I figured out the IVTC now but I how do I encode those then, it doesn't make a whole lotta sense to encode them interlaced right?
Next thing is an interlaced PAL dvd source? Do I deinterlace that or does that work thru IVTC as well?

[adam]

If your working with PAL DVDs then your process will be very simple. You didn't mention what programs you are using but the most common method is just dvd2avi-->TMPGenc. So preview the movie in dvd2avi. It will tell you if it is interlaced or progressive. Make sure forced film is off. Use dvd2avi to create the d2v file and import this into TMPGenc. On the advanced tab set it to progressive or interlaced depending on what dvd2avi told you your source was. Make all your usual settings and encode. CVD and SVCD support interlacing, and if your source is interlaced there is really no point in deinterlacing. Also IVTC really only applies to NTSC material. So just keep your output the same as your source and you should be fine.

To try to answer some of your other questions, I believe most PAL dvds are progressive but some are interlaced. With the exception of anime and tv series, almost all NTSC DVDs are essentially progressive. The stream itself is interlaced, meaning that each frame has been split into two fields, but the fields are displayed at the same time as opposed to one after the other. The result are progressive frames which you can essentially just treat as regular progressive footage. SVCD, CVD, and DVD support both progressive and interlaced material. As I suggested before, with PAL DVD sources, it really doesn't matter if its progressive or interlaced as long as you encode it the same way as it originated on the DVD. With NTSC DVDs its really completely different.

Without getting into all the details, since it seems you probably are just using PAL sources anyway, converting to NTSC is problematic. Film originates at 24fps and NTSC is 29.97fps. You can't just speed the film up that much. So the frames are split into fields and some of the fields are duplicated, in a 2:3 pattern. Since you are adding fields, essentially creating new frames, you don't lose sync and the playback speed doesn't change, and since you are duplicating such a small piece of info at a time, the human eye doesn't notice. The problem with this method is that new frames are created so when you encode it your bitrate gets spread out further, about %20 further. This substantially decreases quality. So DVDs, SVCDs, and CVDs have what are called pulldown flags. You encode at 23.976fps (just a slowed down version of film) and insert a flag into the stream which instructs the DVD player to do the telecine (the conversion process I just described) and it does it all in real time. So like I said, almost all NTSC DVDs are like this. If you use the forced film option in dvd2avi then it will bypass this pulldown flag and export the 23.976fps footage as it is stored on the DVD. This is the preferred method of making an NTSC SVCD or CVD, and also a VCD.

IVTC is just the process of reversing the telecine. You remove the fields that were duplicated which brings your footage down from 29.97fps back to 23.976fps. This only works if the standard IVTC pattern was used in the first place, but there are advanced IVTC algorithms which essentially just try to remove any duplicate fields. How well this works largely depends on how the film was telecined. Like I said, luckily IVTC is rarely needed for DVD movies. Actually the extra's on the disk are almost always 29.97fps but they always seem to use standard IVTC patterns, so they are not hard to IVTC. In my opinion the best and fastest way to IVTC is with decomb.dll through avisynth.

Sorry this post is so long, its hard to describe this stuff otherwise.

[flobbo]

Well, thanks for this in depth information.
I figured out the whole NTSC story by now but I am still having problems with creating a reasonable quality PAL cvd or svcd. My source is an interlaced 4:3 movie from a DVD and when I encode it is get, what I would call, jump frames. For example, there is a conversation between 2 people going on and when the camer angle changes to the person currently speaking there is a blip frame between the 2 camera positions. It is hard to explain, I was able to track this problem down to those frames being 1 interlaced frame of 2 frames being blended into each other. And svcd can't handle that apparently.
Any ideas for that?