[FFmpeg-user] Filter to chain to handle progressive/interlaced/telecined

[Wesley Wen]

We're working on generating FFmpeg command to transcode a set of files. The
file would be progressive, interlaced, or telecined (23.98 -> 59.94i);
there is no mixed content, i.e. progressive + interlaced. We want to have
one FFmpeg command to deal with those three kinds of content (if possible).
After doing some research, I prepare the command as below:

ffmpeg -i source.ts -c:v libx264 -vf
fieldmatch=combmatch=full,idet,yadif,decimate,scale="trunc(oh*a*sar/2)*2:480",setdar=dar
output.mp4

And here are my questions:
* Is the filter chain ideal for our purpose?
* How can I specify the length of closed GOP? I used to use -g to specify
the GOP length as same as fps. However, I might not know the fps without
parsing it. And the real problem is telecined, I want the result file to
have closed GOP = 23.98.

Thanks,
Wesley