Interlacing progressive content

[microchip8]

Hi,

I tried searching for the right answer here but I couldn't find anything useful for me. Maybe my keywords are just bad :/

When one wants to interlace progressive content during the encoding, should one also double the output frame rate? I'm familiar with the 'phase' and 'tinterlace' filters of MEncoder (on Linux) which I use like this...

-vf phase=t,tinterlace=2

I did a small test on a trailer, one time keeping the original frame rate (25fps) the other time doubling it with -ofps 50

The first test, after the encoding was done, the interlaced content looked just fine. However, it had a very very tiny amount of jumpiness in it (hardly noticeable but still)

The second test, with -ofps 50, the jumpiness disappeared. So I'm a bit of confused about which procedure is the right one... with -ofps set to double or without -ofps which keeps the original frame rate of the progressive content?

[Blue_MiSfit]

No point on interlacing 50fps stuff to 50fps.

Interlace it to 25fps, which is thus 50 fields per second.

If you get jumpiness, that's probably because you're viewing interlaced content on a progressive display, which without proper deinterlacing on playback won't look right.

~MiSfit

[microchip8]

so basically you're saying that there's no need to use the -ofps flag to double the output frame rate of the encoding when interlacing it?

[Ebobtron]

There is reason to do nothing, a progressive frame is by definition a single whole picture not two in one. Played in a DVD player a progressive frame is played 1st field 2nd field of your progressive frame unless you send the output to a progressive scan display.

If some frames are progressive and some are interlaced it may only matter to the encoder.

[2Bdecided]

In a "PAL" (50Hz) country you should most certainly "do nothing" with 25p sources. Put them straight onto DVD as they are. That's how all films are done.

Cheers,
David.

[microchip8]

In a "PAL" (50Hz) country you should most certainly "do nothing" with 25p sources. Put them straight onto DVD as they are. That's how all films are done.

Cheers,
David.

Yes I know that, but that was not my question... I'm trying to understand how to interlace a progressive PAL content (just out of curiosity) and my question was if one should change the output frame rate during the encoding so the final file will be interlaced @ 50 fps.... or is it just interlace without setting the output frame rate to double so the final file will be interlaced @ 25 fps

[Didée]

Conversation during a safari:

- How do you shoot a blue elephant?

-- No clue.

- To shoot a blue elephant, you use the blue elephant rifle!

- Now, how do you shoot a pink elephant?

-- Aahh ... with the pink elephant rifle !?

- No. You hold the proboscis of the pink elephant until it becomes blue. Then you shoot it with the blue elephant rifle. (Note I'm absolutely against shooting elephants! - just love this jokes' punchline)


There is no reason at all to interlace progressive content. If you have progressive 25fps content and want to "interlace it for curiosity", then you have to interlace it to 12.5 fps. (Whatever that might be good for.)

Not sure how to do that with Mencoder ... with Avisynth, you would do it by

SeparateFields() .SelectEvery(4,0,3) .Weave()

[SeeMoreDigital]

I'm curious.... Why do you need to interlace a progressive source?

[microchip8]

LOL @ the convo

yeah i know, i sometimes ask stupid question but it's cuz of limited understanding. I know interlacing is bad but i'm just playing and trying stuff out...

so you say that the frame rate should be decreased to 12.5 fps for a PAL movie when interlacing it... so how are 25fps PAL interlaced movies made then? are they shot at 50fps progressive and then interlaced which brings their frame rate to 25fps?

[microchip8]

I'm curious.... Why do you need to interlace a progressive source?

I don't want to interlace it and keep it that way, I'm just trying stuff out and learning how it is done :)

[communist]

so how are 25fps PAL interlaced movies made then? are they shot at 50fps progressive and then interlaced which brings their frame rate to 25fps?
Those are shot with a video camera that records 50 fields (half-height frames) per second, which are recorded intertwined into each other.. or simply interlaced, mixing 2 fields into 1 frame -> 50 fields -> 25 frames.

Each field has unique motion. Splitting a progressive frame into 2 fields will give you 2 fields with no motion in between the two. Splitting a interlaced frame into its 2 fields will give you two fields with motion in between the two.

Dont know if I explained it right but there is little sense in trying to interlace a progressive sequence.

[Didée]

so you say that the frame rate should be decreased to 12.5 fps for a PAL movie when interlacing it... I'm not saying "it should" ...

so how are 25fps PAL interlaced movies made then? are they shot at 50fps progressive and then interlaced which brings their frame rate to 25fps?
Exactly that. True Interlacing means "store the doubled amount of motion states per second, with halved spatial resolution".
To create a 25fps interlaced stream, the process has to start out with a 50fps progressive input.
If you start with 25fps progressive input, then doing the "interlacing process" literally, it will necessarily produce a 12.5fps interlaced result.

[microchip8]

I see, so as communist said, interlaced content is shot with a camera which already produces interlaced footage by default. I thought that they make from progressive content interlaced by applying some procedure and then put the content on DVD.

so if I want for example to interlace a 25fps content, then I also have to up its frame rate to 50fps during this procedure

what I did is just apply the phase=t,tinterlace=1 filters on a progressive trailer and it produced interlaced content at the same frame rate. Though I did notice that it has a tiny amount of jumpiness in fast motion scenes. When I did the second test on the same trailer, only this time I doubled its frame rate, this tiny amount of jumpiness completely disappeared and the trailer was running smoothly... It's a trailer of "Untraceable" which has exactly 24fps as frame rate (not 23.976)

Below is my first experiment (the one without doubling the frame rate during the interlacing procedure). I guess the file below if wrongly interlaced then since I didn't up its frame rate

http://www.fileden.com/files/2006/11/28/434355/Xvid.mp4

A further question. Which is the preferred order of frames during the interlacing process. Should it be odd frames output, even are dropped, or should it be even frames output and odd are dropped?

Btw, I'm just experimenting here, not that you guys think I'm actually interlacing my encodes or something. I'm just trying to learn how to do this and learn how the phase and tinterlace filters work :)

[noclip]

Oh how I yearn for the day interlaced video is relegated to museums and tech history texts.