Output to Blu-ray&Projector: why use 23.98fps?

[Cal Bickford]

I'm shooting in Canon's 24f, if my final output is going to be to blu-ray and a progressive digital projector which can both display 24fps - other than being able to monitor on an external ntsc display is there any point in editing in a 23.98 timeline over a straight 24fps timeline?

[Mike Barber]

Originally Posted by Cal Bickford

I'm shooting in Canon's 24f, if my final output is going to be to blu-ray and a progressive digital projector which can both display 24fps - other than being able to monitor on an external ntsc display is there any point in editing in a 23.98 timeline over a straight 24fps timeline?

Because, IIANM, your footage is really 23.98, not 24 fps. When we're discussing many video cameras (DV, HDV and HD) that shoot "24", we are really rounding up from 23.98. Such is the case with your Canon, I believe.

[Cal Bickford]

So is Blu-ray's native framerate 23.98 then? I thought this was the frame-rate used on standard interlaced dvds while hd/blu-ray used 24fps...?

[Mike Barber]

Originally Posted by Cal Bickford

So is Blu-ray's native framerate 23.98 then?

This is what it says in the official whitepaper (page 17, table 3.3):

"Video streams shall be MPEG-2 video format (ISO/IEC 13818-2) compliant, MPEG-4 AVC video format (ISO/IEC 14496-10) compliant or SMPTE VC-1 video format compliant.

The video formats shown in Figure 3-3 can be used for BD-ROM video streams.

[... for HD:]

1920x1080x59.94-i, 50-i (16:9)
1920x1080x24-p, 23.976-p (16:9)
1440x1080x59.94-i, 50-i (16:9) MPEG-4 AVC / SMPTE VC-1 only
1440x1080x24-p, 23.976-p (16:9) MPEG-4 AVC / SMPTE VC-1 only
1280x720x59.94-p, 50-p (16:9)
1280x720x24-p, 23.976-p (16:9)"

You could pullup your footage from 23.98 to 24.00... but then you may have audio issues to address. Is it worth the effort? That's your call.

[Cal Bickford]

great info thanks Mike! So it looks like Blu-ray does support 23.98fps - This is completely backward from what I thought initially. So where would the advantage be in editing in a 24fps over a 23.8fps timeline other than the ability to sync to a drop frame timecode? Is there any?

[Mike Barber]

Originally Posted by Cal Bickford

great info thanks Mike! So it looks like Blu-ray does support 23.98fps - This is completely backward from what I thought initially. So where would the advantage be in editing in a 24fps over a 23.8fps timeline other than the ability to sync to a drop frame timecode? Is there any?

IIRC, there are higher grade cams (VariCam, Viper, etc... not absolute certainty which) that do record 24fps (as in 24.00), so you would want to edit on a 24fps timeline, not a 23.98fps timeline.

I understand why people like to round up and speak of 23.98 as 24 -- it rolls of the tongue much smoother than 23.98 -- however it does easily lend itself to confusion since there is a difference between 23.98fps and 24fps. In the printed world, i wish people would just stick to saying 23.98 and not 24, when it is really 23.98 -- even if it means an extra three keystrokes (and I will readily admit to having done this myself, though I try to make a conscious effort not to). ;-}p

Perhaps I'm too knit-picky about technical clarity... I did get somewhat jumped on once for pointing out that 1920x1080 and 2k are not the same thing (sure they're close, but they are different). I just think there is already enough headiness when it comes to the technical that we don't need to add to it with lazy communication.

[Cal Bickford]

I agree - there is an amazing amount of technical information that can be absorbed on the internet, it just seems that you have to spend most of your time sorting out the misinformation. Anyways, thanks for helping me clear this up!