Today I was faced with a problem of creating an interlaced NTSC video (“30i”) from progressive HD footage, in my case 60p – that is, 60 progressive frames per second. A quick web search brought up a tutorial from Creative Cow by Marco Solorio, where he converts a 30p footage into a 60i video. Unfortunately, his process doesn’t work when the footage is already at 60p. So, here are a couple of ways that worked for me.

The Apple Motion Way

The most reliable, in my opinion, is to pipe the footage through Apple Motion. This flow will also work for footage other than 60p. Here are the steps:

  1. Create an interlaced (30i) sequence in Final Cut
  2. Drop your 60p footage in it and do the necessary scaling and positioning adjustments (in my case, I had to scale the HD 16:9 footage to fill the SD 4:3 frame)
  3. Control-click (or Right-click) on the clip in the sequence and choose “Send to -> Motion Project…”
  4. Choose the file name for the Motion project, make sure “Embed Motion Content” box is checked. Press “Save”.
  5. When Motion opens, it should already be preset to your sequence output format (30i). If your original clip is not 60p, you can set Frame Blending to Optical Flow in the Properties / Timing pane (otherwise leave it “off”). In the preview you should see the jagged lines for any moving objects in your clip – that’s exactly what you want.
  6. Save the Motion project and return back to Final Cut. The original clip should now be replaced by the perfectly interlaced Motion clip.

Motion (unlike Final Cut) does not de-interlace the frame for display, so you can see the actual raw interlaced fields as they are. It is also much smarter about retiming, and will grab the correct frame of a 60p footage for each field automatically.

A fair word of caution – if your clip is more than a few seconds long, don’t try to render it in Motion. Or, before you do, reduce the Memory Cache setting to something low, like 20%. Otherwise Motion will hog all your available RAM and will take hours to render because your computer disk will be thrashing. However, rendering the same clip within Final Cut will work fast and furious with no noticeable memory overhead.

The Final Cut Way

Now, if you do not have Motion installed, you can still do it in Final Cut with a little help from Cinema Tools.

  1. Open your 60p clip in Cinema Tools and conform it to 29.97 fcp. The clip will now play at half the normal speed.
  2. Import the clip into the Final Cut 30i sequence and speed it up by 200%. Make sure your sequence has frame blending turned on. You are done.

The key here is the speed up by exactly 200% with frame blending. Turns out, Final Cut can do frame blending for individual fields of the interlaced frame, but only when the footage is retimed. If you try to drop an un-retimed, un-conformed original 60p footage in the same sequence, the fields will be pulled from one and the same progressive frame, which is not what you want. This was the problem somebody posted in the comments to the above mentioned article.

Instead of Cinema Tools you can use any other software that can conform clips to the required frame rate (Compressor, Adobe AfterEffects, etc.).