[FFmpeg-user] ffmpeg and use of the ildct flag in progressive encoding

[Nik Armstrong]

On 2023-12-14 12:50, Nik Armstrong wrote:
> I've encountered a scenario where someone else has programmed an
> ffmpeg encoding command with flags that seem puzzling, and I'm having
> difficulty understanding their purpose.
> 
> The command in question is:
> 
> ffmpeg -loglevel info -y -r 29.97 -start_number 0 -i
> image_sequence_%4d.png -vcodec dnxhd -vf
> format=yuv422p10,colorspace=bt709:iall=bt601-6-625:fast=1 -b:v 220M
> -flags +ildct output.mov
> 
> I've been struggling to find information on what the addition of ildct
> does to the output. It appears to be influencing the media to perceive
> it as interlaced, even though it is, in fact, progressive. Using the
> flag ildct seems counterintuitive and unproductive.

The ildct flag appears only to be making the output file "think" it is 
interlaced, when it is, in fact, progressive. It does not seem to be 
doing anything to change the footage (quality-wise and it's still 
progressive). Since someone other than myself set the flag on this 
command, I am trying to figure out what effect, if any, taking it off 
will do to the output.
Regards, Nik