HV20 1080p24 HDV easy setup with 1080i60 compression? = smaller files?
 

Even though I use FCP almost every week of my life, I admit that I am no guru and there are aspects of it which I don't fully understand. Recently I was trying to import some 24p footage from the HV20 into FCP 6.0.1 and came upon something odd.

Getting true 24p footage from the HV20 into FCP in itself is a small bit of trouble because the interlacing needs to be removed by an external program. There are a number of options, but Apple suggests Compressor and that's what I was using to remove the interlaced frames and return the footage to all progressive frames. The question I have came up as the result of somebody messing up the prefs on the one system I happened to be using that day, but the result was interesting and I wondered if somebody could explain it to me.

For whatever reason, the Easy Setup for "HDV 1080p24" had the "Quicktime Compressor" set to "HDV 1080i60" instead of "HDV 1080p24". What I mean is that when selecting the "HDV 1080p24" "Easy Setup" to set up the sequence settings, the "Editing Timebase" was correct at 23.98, as was the aspect ratio and the rest, but under "QuickTime Video Settings" the compressor was set to "HDV 1080i60" instead of the devault of "HDV 1080p24"

Because of this fact the reverse telecined clips, which were all 23.976 timebase and compressed with "HDV 1080p24" compression, would all stutter with repeated frames in my "Easy Setup" sequence. When they were placed in a timeline with the matching settings, they worked fine. And when I went back to compressor and deinterlaced with an output of 23.976 fps but compressed with "HDV 1080i60", the clips would work fine in the sequences created by the altered "Easy Setup".

The thing is, they worked perfectly, but with a smaller filesize. I counted frames and looked at video clips side by side. The 23.98 "HDV 1080p24" files looked EXACTLY like the 23.98 "HDV 1080i60" files. They are frame identical as long as they were playing back in the appropriate sequence OR played back in Quicktime, but the clips with the 'wrong' settings are at 80% of the file size.

What is happening here? How does encoding with the "HDV 1080i60" even work, let alone result in smaller files with the exact same frames?