slow motion by interlaced to progressive conversion?

[menczel]

Hi,

I am new to this forum and don't have much experience in video editing / conversion. Please, forgive me if some of my questions or ideas seem primitive or trivial.

The problem I want to solve is to produce slow motion videos for motion analysis in sports (in my case table tennis). Unfortunately, professional slow motion video cameras are quite expensive, our club cannot afford to buy a camera costing several thousand dollars.

Many affordable video cameras will produce interlaced video at 60 fps (1080/60i). My idea is to take the interlaced frames and treat them as consecutive independent frames, and play the resulting sequence at 30 fps. Obviously, because the vertical resolution is halved, some kind of line doubler or video re-sizer must be used for producing the final video.

My questions are:

Is this feasible to do at all?
If yes, which particular video editing tool would be the best for the job?
What kind of pitfalls should I be aware of if I attempt such a conversion?

Update: I found (by accident, really) a link where the above procedure is described. Here is the link:

http://avplumber.wordpress.com/2009/09/04/60i-to-60p-to-24p-slow-motion-conversion-and...solution-myth/

However, they used Adobe After Effects that I am not going to buy for several reasons

So scratch question 1, but the rest is still valid.

Thanks!

Laszlo Menczel

[jagabo]

Yes, it's called "bobbing" the video. The trick is in converting two half pictures (every other scanline of the frame) into two full pictures. There are many techniques ranging from simply duplicating scan lines, simple interpolation, through much more complex techniques that look at both fields, even the frames before and after, to fill in the missing scan lines.

VirtualDub has several methods built in and also some third part filters. AviSynth has the best bob filters -- like QTGMC.

AviSynth also has the ability to add motion interpolated frames between existing frames. It works well for some types of motion, not so well for others.

[menczel]

Hi,

Thanks for the quick reply and the tips. I will try the programs you mentioned.

Another question: Is there a video player that would play interlaced videos as non-interlaced, but at half speed? I mean, it would do the above mentioned conversion on the fly. This would simplify matters tremendously. Maybe Videolan can do the trick. If not, I can request it as a new feature IMHO it would be rather useful for a lot of people.

[jagabo]

VLC has several bob type deinterlace algorithms (try Yadif 2x). It also has the ability to slow down the frame rate (Playback -> Slower, you can select it several times to get slower and slower playback but it will just be repeating frames, aside from the initial bob).

Various deinterlacing algorithms (some only single rate):
https://forum.videohelp.com/threads/292642-Deinterlacing-Tips-and-Good-news-that-i-foun...=1#post1784755

This post has an AVI file showing different deinterlacing methods (all double rate):
https://forum.videohelp.com/threads/322333-Lines-on-my-rendered-videos?p=1996578&viewfu...=1#post1996578

This post has an example of a simple bob (bob.avi) and a motion interpolated slow motion (slow.avi):
https://forum.videohelp.com/threads/243743-Super-Smooth-Slow-Motion-from-standard-DV-ca...=1#post1442442

Motion interpolation doesn't work well for complex motions. The technique has improved a bit since then.

[menczel]

Hi,

Thanks for the info. Probably the best solution is to get a camera that can record progressive video at 60 fps, transfer the material to a PC and slow it down in the Videolan player to 20-25 fps. If only short segments (2-3 minutes of video) are used, one can probably see the result within a minute.

[jagabo]

There are some fairly inexpensive high def camcorders that can record at high frame rates with small frame sizes for short periods of time. Some of the Sanyo Xacti models for example sell for less than $500 and can record at 448x336 at 240 fps, and 192x108 at 600 fps. Go to YouTube.com and search for "slow motion camcorder" and you'll see lots of sample videos. They also shoot 1920x1080 at 60 fps.

http://www.youtube.com/watch?v=vhQVfY7q5dI
http://www.youtube.com/watch?v=hgXndRuWs-M

[menczel]

Hi,

Thanks for the camera info. The only problem is that high speed recording is time-limited, these cameras can take only a few second long videos at high speed. This is a bit strange and seems to me an artificial limitation (maybe for commercial reasons?). After all, an SD card of several GBs could hold a much longer video even when recorded at high speed.

The best solution to my problem appears to be that I get a Samsung camera that can record 720p@50 videos in a PC friendly format (MP4 using h.264 but not AVC) and play it on a PC at half speed. I think MPLayer is perfect for playing, its controls are much simpler than those of Videolan (although the latter can also do the job).

[budwzr]

Forget about interlaced video. That's old skool, and sucks.

The Kodak Playsport shoots 720p60 and has stabilization and can be mounted to a tripod. Also, the GoPro HD Hero shoots 60p, and has a super wide lens. Both take very good video, and there is no time limit.

The problem is going to be that a golf swing is so fast that you really need 120fps or faster. However, you can stretch the time and interpolate the frames and see how it looks. But that takes time, and you won't be able to review the swing right there on the course.

If you play back at half speed, the software will simply blend everything on the fly, and that's going to be blurry.

Be careful what you buy. There are unscrupulous vendors that sell old stuff as new technology. The camera market is evolving so fast, you really have to pay attention.

[edDV]

Casio also makes the Exilim line of inexpensive high speed cameras.
http://exilim.casio.com/digital_cameras/High-Speed

Up to 1000 fps.

[budwzr]

Casio also makes the Exilim line of inexpensive high speed cameras.
http://exilim.casio.com/digital_cameras/High-Speed

Up to 1000 fps.

Hey, that looks pretty good. And good reviews at Amazon. Hmmm...

And it looks like a putz camera, so you can blend right in as a tourist. If you have a pro looking camera, everybody gets nervous.