This is the most effective deinterlacing tool when the footage is a video transfer of a film. This can be used to solve the problem, i.e., undo the damage caused by making film into a TV broadcast. That process came about because film is at 24 fps while TV is at 29.97 fps and fields are at 60. So the film was converted from 24 fps to 60 fps. Roughly speaking, converting every 4 frames into 5 frames plus a slight slow down in speed. Then the 60 fps was down-sampled to 30 fps by extracting odd and even lines and interlacing the lines. This process is referred to as three-two pull down (3 : 2 pull down) in filmmaking and television production for the post production process of transferring film to video. The three-two pull down is where the telecine adds a third video field (a half frame) to every second video frame, but the untrained eye cannot see the addition of this extra video field. The IVTC effect is primarily a way to convert interlaced video to progressive video. It reverses the effect of three patterns of interlacing. In the next lines A, B, and C represent fields.
A AB BC CD D
AB CD CD DE EF
The first two options are fixed patterns and affected by the pattern offset and odd field first parameters. The last option creates several combinations of lines for each frame and picks the most progressive combination. It is a brute force algorithm that is trying to resample the lines. This technique does not rely on a pattern like other techniques and is less destructive but the timing is going to be jittery because of the lack of a frame rate reduction. In order to smooth out the timing, you need to follow inverse telecine with a decimate effect.
The CINELERRA-GG Community, 2021