I have been researching a problem, and have hit a wall.  It seems that this forum is the best place for an answer, and MichaelP is the man for the job.  Where to start?  I am a video assist operator in the motion picture industry.  We are the guys who record from the video tap on the film camera and display and playback the images for the director, DP, et. al.  We also keep an on-set library of our tapes for future reference.  I am among a small group of video assist operators who do pre-editing on-set, (mainly action cutting and effects compositions.)  I have been using Avid Xpress DV for about three years on set.

 

(The following discusses NTSC, as that is the format of my next project.  I will tackle PAL when I do my next PAL show.)  Modern video taps create a “flickerless” 30i signal by applying a 2:3 pulldown on the 24fps (not 23.976fps) image that they receive.  In the past, I have just captured the footage live from the video tap on the A camera and from tape for all subsequent cameras, and edited in 30i for a rough idea of what the cut would look like.  If the director wanted to show the editors my rough cut, or if the director wanted a cut scene available on set, we would do this via video tapes.  Admittedly low tech, but state of the art these days.

 

I have just moved on to Pro HD 5.2.2 with Mojo to take advantage of the ability to show 24p footage from the editors on set for the powers that be.  I can now accept media files and bins from the editors, and show these on set.  Now comes the problem of editing footage from the camera tap, as we shoot it, with the editor’s footage.  In an ideal world, I would capture the video into 24p and be able to cut it in, but the signal from the camera is 24fps pulled down to 30i with 2:3, and I have no way of telling Avid which frame is the A frame during capture.  There is no available reference from the camera tap.  To locate the A frame after the fact on each take and do a transfer to 24p would be too time consuming on set, not to mention that it’s 24fps (not 23.976fps) that is being pulled down, and this shifts the cadence slightly from the normal.  Trust me, the results are far from acceptable.

 

So it seems that my only solution to get the two rates together is to transfer the 24p editor’s sequence to a 30i sequence.  I have seen solution that included re-digitizing the 24p footage, but this is not an option.  I can get the 24p footage into my 30i project by exporting a QT reference from 24p, and importing it into my 30i project.  The way that Avid accomplishes this is by doubling every fourth frame.  A B C D from 24p becomes A B C D D in 30i.  This is actually acceptable for on set display.  The problem now is how to get the media AND the sequence translated into 30i.  My only option now is to hand recreate the sequence using the transcoded 24p media in 30i.  The 24p clips have timecode burned onto the frame, so that will help, but a true sequence would be much better.

 

Well, what do ya’ll think?

Video taps on film cameras don't insert timecode or flags into the stream to indicate what the cadence might be at any time. The Avid expects some sort of reference between frames/cadence and timecode to accurately and repeatedly capture the right frames. This is possible with HD camera and camera backs from Evertz and others that create a DV25 downconvert with embedded audio and timecode and can also create NORMAL and ADVANCED pulldown.

In your case, you are getting media from a true 24 frames project, the on set is giving you true 2:3 pulldown at unknown relationships at 23.976 etc. There is no real way to capture correctly in such a situation.

Here are a couple of suggestions:

.1) Take only the sequence from the editors and import that with the 24+1 look in a 30i project so there is no need to try and recreate their edit.

.2) The next release of Avid products in Q2 includes a real time field removal during play - drop the effect on the badly captured material from the tap - it removes a field during playback and will not have that stutter effect when playing. Albeit it will only be a field doubled frame, the hit in softness more than makes up for the stutter that could kick off an epileptic attack.

Hope this helps for now.


Michael

Interesting. We are having the exact opposite problem right now at our post house. We recently upgraded to Avid Xpress HD w/mojo (although kinda feels like the mojo is worthless in the HD world right now.) We have been shooting heavly on a Varicam for almost two years now and want to re-output some of the programs useing the DVCPRO Codec available in a 720p 23.97 project (Trying to avoid going to 1080i since the original is 720p) so far we have not been able to find a workaround to recapture the cansolidated master clips in this diffrent frame rate. Any thoughts. Is this even possible. Wishing 720p 59.97 had an mxf capture option.

VFR is a special case capture at this time. Please whitepaper on my website at:

http://www.24p.com/VFR.htm

And make sure you read the caveats and current limitations for recapture.


Michael