9 Replies Latest reply on Aug 28, 2012 10:52 AM by Pierre Devereux

    Time manipulation

    Pierre Devereux Level 2

      Hi guys,

       

      I have taken a look at some of the Video-copilot tutorials on time manipulation, and have a question or two around After Effects and frame rates.

       

      The Panasonic camera I am using, according to the documentation, can record several frame rates as it has Variable Frame Rate capabilities. Footage shot native to the camera, direct to card only records at around 192mb per second (24 MegaBytes) and I dont believe that, that is very good. If I record to an external device, the same 10 second test results in 1880mb per second (235 MegaBytes). This is obviously a great deal better, and contains a lot more information to allow for more post work.

       

      The problem I am finding, is that according to the documentation, you cannot record higher than 30FPS to an external recording device, as HD-SDI cannot handle data rates greater than 1080/30P. If I use the device ( a samurai recording device) apparently, each frame is automatically embedded as a field into a 1080/50i data stream.

       

      obviously when I import this directly into After Effects, I need to re-interpret the footage and select the correct field first - the motion is then pretty good as slow motion (if imported into a standard 25fps composition - I am working in the land of PAL) with the obvious motion issues (strobing or skewing). My question is this:

       

      Is this the right way to go, or should I record standard 25fps from the camera to the recording device ( at a data rate of 1766mb per second (220.8 Megabytes) ) and purchase a third party time manipulator like Twixtor to do the slow downs?

       

      There is an interresting paragraph in the camera documentation that I dont quite understand though, and I am also not familiar with the software mentioned - if I may, I would like to quote the paragraph (ok, Ill paraphrase) and see if someone can explain it a bit better?

       

      "With post manipulation, you can get 1080/60p out of the AF100. the camera already records at 60 progressive fields per second. when the camera is in 1080/24p or 1080/30p and a frame rate of 60 is selected, the camera records 60 discrete frames each second. the file would have a playback rate of 24p or 30p encoded in it, but what if you changed the playback rate? say, what if you went into Cinema Tools and "Conformed" the footage to have a timebase of 59.94p instead of 29.97p or 23.976p? obviously it would become full fledged, live  1080/60p footage. 60fps played back at 60fps = full screen, full quality 1080/60p. and of course the same applies to 50Hz mode - resulting in full fledged 1080/50p"

       

      The camera settings in Pal-land are PH 1080/50i, PH1080/25P, PH 720/50P and PH720/25p - Since the best quality only give 50i, the paragraph above confuses me a bit, how would I get 1080/50p from it? - of course, I am assuming that the camera is set to 1080/25p and the Frame rate is set to 50FPS to allow the above mentioned outcome. anyway, once again, maybe not an entirely AFter Effects question, but any help would be greatly appreciated.

       

      Pierre

        • 1. Re: Time manipulation
          Dave LaRonde Level 6

          Forget the 24p thing.  It will NOT yield the results you want.  It actually shoots 23.976 frames per second, but evenly spreads them across 59.94 frames/sec.  This is the classic 3:2 pulldown you may have heard about.  Thus you do have 59.94 frames/sec, but only 23.976 DISCRETE frames/sec.  That's not good for slo-mo.  It's not much good for slo-mo. 

           

          24p isn't much good for anything if the footage is still at 59.94 because you need to remove the pulldown before any time manipulation is done.  And where does that leave you?  At 23.976 frames/sec... which isn't good for slo-mo.

           

          The problem with time manipulation is slowing things down, yet retaining image quality.  This calls for the highest frame rate possible.  In your case, that would be 720p50, which would let you reduce speed by a factor of 2 with no loss of image quality.  Using a plugin like Twixtor, you could slow it down even more.

           

          The more discrete frames per second you have, the slower you can go.  This is why Phantom cameras exist: they easily can shoot 1200 frames/sec.

          • 2. Re: Time manipulation
            Rick Gerard Adobe Community Professional & MVP

            I'm not real sure what you're asking here. If you are intending to do slow-motion then record the highest frame rate you can. If you want time to match real time the footage must be interpretetd at the same frame rate that was used to shoot it. If you want to change the speed you have to be understand what is going to happen when you change the frame rate interpretation. Let me explain.

             

            If you then place 10 seconds of 60 p footage inside a composition that is 20 fps, or 24fps, or 99 fps the shot will still be exactly 10 seconds long. If the frame rate is higher than composition frame rate some of the frames will be dropped. If the frame rate is lower than the frame rate of the composition some of the frames will be duplicated. Motion artifacts from dropping frames are not as noticeable as motion artifacts caused by duplicating frames. Frame blending and other techniques available in After Effects mitigate these problems. Third-party solutions like Twixtor can do a better job than the tools that come with AE but may not be necessary unless you plan to slow footage way way down.

             

            Let's talk first about progressive footage. If the frame rate is higher than the frame rate of your composition, and you're planning to use the built-in tools, the proper technique is to match the frame rate of the composition. If your composition is 24 FPS then interpret the footage at 24 frames per second. If the composition is 30 frames per second or 29.97 FPS then match those numbers. Then ten seconds of 60p footage in a 30fps comp would play for 20 seconds, or be at 1/2 speed. Ten seconds of 60p footage in a 25 fps comp would play for 24 seconds. If you are using AE's built in tools then this is your best option no matter how you want to change the playback time.

             

            If you are using a third-party time manipulation tool like Twixtor, then you must follow their instructions. Twixtor will only work properly if you match the frame rate to the actual frame rate of the footage.

             

            If the original footage is interlaced you have a different kettle of fish. Does 50i footage really have 100 fields per second or are there only 50? Is 60i footage really 60 FPS with 120 fields per second or is it 59.97 fields per second at 29.97 FPS? In both cases the latter is true. There's only one way to know for shure. You separate the fields and set the frame rate to your best guess. Then create a new composition with your footage by dragging it to the new comp icon or selecting the footage and choosing New Comp from Footage. Then you open up the comp settings and double the frame rate of the composition (you can do the math in the field by typing *2 after the value that's there). Then step through the footage one frame at a time using the Page Up key. This will tell you immediately if you've interpreted the frame rate correctly and whether or not the field order is correct.

             

            I haven't run specific tests on your camera or your external recording device but in all likelyhood your 50i footage is 50 fields per second and 25 FPS. IOW, the proper interpretation is most likely 25fps separating fields upper first. Run a test to make sure.

             

            Once you know exactly what you've got, you have three options. My usual technique is to just render this frame doubled comp to a production format so I have no need to deal with interlaced footage and the rest of my production pipeline. The other is to use the frame doubled comp as your footage source for any time manipulation you will be doing making sure that preserve frame rate of nested compositions is turned on. The third option is just to use the properly interpreted footage.

             

            One more thing before I go. If you are using a third party solution you must follow their instructions specifically when you are using interlaced footage. The footage must be properly interpreted for any third-party solutions to work correctly.

            • 3. Re: Time manipulation
              Pierre Devereux Level 2

              Hi Dave,

               

              Thank you for the reply. Because I am shooting in 1080/25P, in a PAL (50Hz) territory, will this still be the same? Does 25p not play back at 25FPS? We are shooting for TV, and the broadcast rules state 1920X1080 50i footage for them. Would that not make the 720p50 unacceptable? The ast question then, is, if I have the choice to shoot at 25P or 50i, should I not choose 25P for better quality?

               

              Thank you once again for your response - i have the sinking feeling the next few weeks are going to be spent on getting to grips with the 3:2 pulldown issues! :-(

               

              Thank you

               

              Pierre

              • 4. Re: Time manipulation
                Pierre Devereux Level 2

                Hi Rick,

                 

                Thank you as well for your detailed response. I am shooting at 1080/25p, but as the documentation states, using the Samurai to record at 50FPS, it stored each frame in a seperate field of a 1080/50i data stream.

                 

                I have tested this, and true enough, placing this footage into a standard 25FPS composition has terrible combing. If I re-interpret the footage with seperate fields, top field first, the combing goes away. the movement is still rather juddery, but I will look into After Effects built in frame blending techniques as suggested.

                 

                What I am trying to achieve, is to film a miniature character at 50FPS and slow it down, not terribly, but enough to make the subtle movements we are introducing give the character a slightly more "life-like" look.

                 

                I think for now, for the next tests, ill try to shoot at the higher frame rate, seperate the fields in a new composition and render out best quality as you suggest in the first option, I will see where that leaves me.

                 

                The next thing, is to wait a bit and see if anyone else replies - I need to know if it is worth the terrible exchange rate from SA rands to USA Dollars for Twixtor! :-)

                 

                Thanks again Rick

                 

                Pierre

                • 5. Re: Time manipulation
                  Rick Gerard Adobe Community Professional & MVP

                  the movement is still rather juddery

                  It shouldn't be if your frame rate matches the comps frame rate. You should be getting a frame for a frame. If not, then there's a mis match somewhere.

                   

                  Did you try the double frame rate comp test? Generally, 50i footage should be interpreted as 25 frames per second with upper fields first.  This footage placed in a 50 FPS composition should give you no duplicate frames. If there are duplicate frames then your camera is not delivering true interlaced footage to your external recorder. The external recorder is simply interlacing 25 identical (progressive) frames. This would actually be the expected behavior. You can interlace anything, but you will only get double the slices of time if your camera is producing interlaced footage to start with.

                  • 6. Re: Time manipulation
                    Pierre Devereux Level 2

                    Hi Rick,

                     

                    Ill try the tests you suggested today at the office, Ill post the results later. So far, Yesterday, just for fun, I took a series of 5 second shots (of my sleeping cat - there was no action anywhere else!) that had some shadow movement. I took a series of different Frame rates, coupled with different shutter speeds. Ill play around with the footage in After Effects and see wht I come up with. I will most difinitely try the double frame rate comp test.

                     

                    Thank you

                     

                    Pierre

                    • 7. Re: Time manipulation
                      Pierre Devereux Level 2

                      Hi Rick,

                       

                      I shot around 24 different tests yesterday with the camera, ranging from Auto settings for frame rate and shutter speeds, to Variable Frame rates of 12, 30 and 50 ( each one with shutter speeds at auto, 1/25 and 1/2000). I did this to test a few things, the available aperture settings to the camera for lighting, the camera's capability of capturing detail in , for instance, a slow running stream of water out of a pipe to the ground and of course, what the frame rates will do in After Effects. I was one of those misguided people, who assumed that recording at a higher frame rate, will magically, and with no extra effort, give me great slow motion in After Effects! :-)

                       

                      After several tests with the footage this morning, apart from confusing myself to no end, I am now able to confirm your comments above. If I take a shot that was done with:

                       

                      1080/25P, Variable Frame Rate of 50FPS, Auto Shutter, and recorded to the Samurai device.

                       

                      and import it into After Effects, I interpret it as 25FPS seperate with Upper fields first and place it into a composition with 50FPS, I get no duplicate frames at all. This means that I am getting discreet frames from the camera to the device. I will also take your advice, and then render this out for usage, therefore giving myself an interlaced free workflow.

                       

                      Now, since I was so misguided with my idea of how this cnforms to time remapping, I will re-look at the built in AFter Effects features to slow time down, and see what I can come up with.

                       

                      Thank you for your input, even though I have not yet solved the slow motion issues (and this is because I have not invested enough time and effort in understanding it yet) you have really helped me a lot to understand more about how the camera and the device record the footage - and how to best import it into my workflow.

                       

                      Thank you

                       

                      Pierre

                      • 8. Re: Time manipulation
                        Pierre Devereux Level 2

                        Hi,

                         

                        I had a pretty good day - still early days, I know, but I like the results so far. I have imported and created the double frame rate comp, and it renders out very well at real time speed. I then use time stretch and other AE built in tools, and am pretty happy so far with the results, As I say, still a lot of testing to be done, but thank you all for the advice. Enjoy the evening (um, or morning, depending!)

                         

                        Pierre

                        • 9. Re: Time manipulation
                          Pierre Devereux Level 2

                          Hi Rick.

                           

                          I think I have solved the issue and lack of understanding around frmae rates - footage VS comps and how they are best used to slow time etc. Thanks to your help above, I was put on the right track, and have found so far, that the following is best:

                           

                          1) Shoot at 1080/25P

                          2) Use Variable Frame Rate of 50FPS

                          3) Capture directly to Samurai device

                          4) Import file into after effects and interpret as 25FPS seperate fileds - Upper field first

                          5) Create new composition from footage - then double the frame rate of the composition (leave footage as interpreted above)

                          6) Render this comp out to a TIFF sequence

                          7) Import TIFF sequence into new composition with a Frame Rate of 25FPS - this now plays back at half speed, smoothly as the above process give me 50 discreet frames.

                          8) I am now free to use Twixtor (a demo version for now - Beware the great X!) to slow it down even more.

                           

                          And that is the workflow for now, to get slow-motion.

                           

                          Thank you once again for all the help - if I can get the overbright issue sorted out now - I am A- for Away!

                           

                          :-)

                           

                          Pierre Devereux