3 Replies Latest reply on Oct 5, 2010 7:15 AM by Mylenium

    Changing frame rate at render time?

    moceandesigns Level 1

      By default AE brings all sequences into the library at 30 fps, and creates new comps at 30fps, and I'm fine with that, im used to thinking in those term.


      This projects final output is an .flv to go into Flash, and play at 15fps.


      I want to render every single one of my frames, which the comps thinks of at 30 fps and write them out at 15 fps.

      So the frame that was at 1 sec in the comp (frame 30) will now be at 2 sec in my flv (still frame 30).



      I cant wrap my head around how changing the frame rate at render time works?  Sometimes I think it works like I want.   -   Sometimes I feel like it throws away every other frame, so frame 30 from the comp is frame 15 in the flv, both at 1 sec, which makes sense, I just dont wan't that at the moment.   -   This last one I rendered did what I want with making a 10sec 30fps comp a 20sec 15fps flv - except the flv is all jerky, 2 or 3 frames are the same, then it skips to 3 frames later and holds it for 3 frames, and so on...






      I'm able to create a holder comp in AE, set it to 15fps, and drag in my 30fps comp, and time stretch it to 200%, and render that out and it seems to work.  But I'd rather skip all that and just say, render all the frames from this comp, whatever it's rate, and apply this rate when your done.  Is that possible?

        • 1. Re: Changing frame rate at render time?
          Todd_Kopriva Level 8

          The time-stretching way is the way to go for what you're trying to accomplish.


          Let me explain a little bit of what's going on under the hood so that you can understand why:


          After Effects thinks primarily in time (seconds) not frames. A composition that is at 30 frames per second will sample the image data from its layers 30 times every second. Similarly, a render item that is at 15 frames per second will sample from a composition 15 times per second.


          So, it's not as if After Effects is holding a bunch of frames that then get distributed across time (which is kind of what you're thinking of, it seems).


          There's lots of information about frame rate here:

          "Frame rate"

          • 2. Re: Changing frame rate at render time?

            Thanks.  I guess I was hoping you would say look here for the "work the way Ocean wants" button, but I guess I'll settle for  someone confirming my wild theories and functional work arounds.


            Appreciate the help.





            While we're not on the subject, is there anyway to set an offset in 'syncronizing nested comps'?  Mostly it seems to work pretty well, but sometimes they get off from each other and it is muy annoying.  I think it has to do with time remapping, or having multiple copys of a nested comp which start at different times.  IIs there anyway to say, look at this layer as the one to snyc times on?


            Thanks again.


            • 3. Re: Changing frame rate at render time?
              Mylenium Most Valuable Participant

              It's actually the same issue that Todd already described - your time-remapping needs to be frame-exact to use consistent results. If there is a minor sub-frame discrepancy because AE works on "real" time, this may result in the wrong frame being sampled. The longer the clip, the more such tiny discrepancies will accumulate and manifest themselves. So in short, you may actually sometimes need to use seemingly odd values to get correct alignment. To make this easier, you may wish to toggle the time readout to frames by simply Ctrl+clicking on it. Also keep in mind, that inputs accept simple math, so you may use frames*frameDuration as the input format, i.e. 50*0.04 will give exactly 2 seconds in a 25 fps PAL project...