Wednesday, December 16, 2015

[Avid-L2] Re: How to convert a file containing 18fps 8mm film frames to 24fps?

 

Cinema tools will restamp a frame rate it it's an I frame codec.  Also QT change has some of that functionality but I believe there are caveats to QT changes frame rate restamping that isn't recognized by all software.  I haven't used the function in QT Change so I may be in error about it capabilities and limitations.  If there was only an expert on it on this list then my Holidays would be complete. Oh wait.....  ;-)



---In avid-l2@yahoogroups.com, <dvcinlv@...> wrote :

> Otherwise, I bet Media Encoder or Compressor (using Frame Controls - Fast retime) would handle this accurately.


Mark, I laid out your solution:

Rate Control: FAST (nearest frame)  <<< I assume this "Fast Retime"
Set Duration   * so source frames play at 24.00 fps

Each second 24 frames need to be placed in the new file. The "nearest" 18fps frame -- closest in time to when a 24fps frame would be output -- will chosen to be output. This works as one frame in every three is repeated: 1:2:1

Frame:     1              2                     3               4             1             2                      3                     4              1
24fps:   0.000      0.042               0.084         0.126     0.168      0.210               0.252              0.294        0.336

              0.0        0.014          0.028  0.028    0.014       0.0      0.014           0.028   0.028       0.014          0.0

18fps:   0.000        0.056  >>>  0.056        0.112         0.168         0.224 >>>  0.224             0.280            0.336

Then I realized I made an error when I said the first file was 18fps. My frame-by-frame film transfer unit's software outputs a file with every film frame recorded as one PsF video frame. Unfortunately, the software tags this file as 29.97fps because, I assume, a QT file needs some frame rate tag and 29.97 is the only valid NTSC frame-rate. So the times aren't every 0.056 as I showed, but 0.033. (I think this is why MC won't work either.)

Your solution would work were there a way to change the source file's frame rate to 18fps without changing any frames in the file. I have utilities that read-out frame rate, but at this minute I can't think of one that modifies a frame rate. Anyone?

I could convert the source file to a folder of numbered images. This eliminates all frame rate information. I could write an AppleScript that copies each image to another folder with every third image copied twice. Now Compressor would output a 24fps file from the second folder of images.

Far simpler would be if an existing utility could be given a string = CCR and it would use this pulldown to make a file and tag it 24fps. 

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Posted by: bigfish@pacbell.net
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