M: Ffmpeg: how do I deinterlace a VOB file when I’m converting it to MP4

G: TL;DR: Use yadif (Yet Another DeInterlacing Filter) with FFmpeg like this:

ffmpeg -i input.vob -vf yadif -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 192k output.mp4

Explanation:

-vf yadif — applies FFmpeg’s built-in deinterlacing filter.
-c:v libx264 — encodes video using H.264.
-crf 23 — sets quality (lower = better, 18–28 is typical).
-preset medium — balance between encoding speed and compression.
-c:a aac — audio codec.
-b:a 192k — sets audio bitrate.

Optional improvements:

If you want better quality, use -vf yadif=1 (single-rate mode = 1 frame out per input frame), or for double-rate (up to 60 fps from 30i), use yadif=1:1.
You can also add -movflags +faststart if the MP4 will be streamed.

Let me know if you want to automate this for a folder of VOBs or tweak for archival quality.

M: If I already have a -vf flag, should I include it in serial, or concatenated it somehow

G: If you already have a -vf flag, you concatenate filters into a single -vf chain, separated by commas. Do not use multiple -vf flags—only one will be used, and the others ignored.

Example:

If you're already using -vf scale=1280:720 and want to add deinterlacing:

-vf "yadif,scale=1280:720"

This means: first deinterlace with yadif, then scale.

Filter order matters:

Deinterlace first, then do scaling or other processing.
If you're adding subtitles (subtitles=...) or overlays, they should usually come after deinterlacing and scaling.

Let me know what your full -vf is and I can help you chain it properly.