6 Replies Latest reply on Sep 28, 2010 1:21 AM by westonwoodbury

    blank frames alpha exporting as black

    westonwoodbury Level 1

      I've noticed this a few times in various projects and can't find any other threads about it.

       

      I'm exporting with alpha channel and want to leave 2-3 blank frames on the front and tail end of the animation, because that's how the live software I'm working with works (it'll essentially sit paused on the blank frames, on top of the video, until play is pressed; so the first few frames can't have the first frame of the animation in it).

       

      Problem is, whenever there is nothing on the screen, AE exports it as if there were a black solid there.  I get 2-3 frames of black, then as soon as the first frame of the animation hits, the black disappears and it's got the alpha channel.

       

      Ideas?

       

      - wb

        • 1. Re: blank frames alpha exporting as black
          shooternz Level 6

          Insert something that you do want to display before your program starts.

           

          ie . dont use alpha frames at the head of the layer!

          • 2. Re: blank frames alpha exporting as black
            westonwoodbury Level 1

            Shooternz,

             

            It can't be anything, it needs to be a blank frame so that nothing shows up on screen.  It's not for before the program, it's for a graphic that is supered during the program.  The frame needs to be blank so that there's not something the whole time that we don't need the graphic.

             

            A workaround to this AE bug would be just adding a couple blank frames to both ends of the sequence in some other program (like PPRO) and exporting it again from there.  Just an extra step that I'm trying to avoid.

             

            It's shown up more frequently in png or tiff sequence renders that I've done, though I haven't tested for repeatability.  In these cases, the workaround would be to have a blank tiff or png image handy and rename/copy it to replace the black frames in the sequence.

             

            I've been experimenting (this time is to Avi Lossless w/ alpha) and it does indeed seem to be a render bug, I can't narrow down a specific cause.  Out of about 20 very similar animations, about 17 of them rendered out clean (blank frames before and after working properly) and 3 of them put black frames instead of blank frames.

             

            I was able to re-render these 3 again, and without really doing anything, it worked with the blank frames working properly.  For one of them I played with undoing some pre-comps (putting everything in the main comp) and thought that might have been the issue when it worked successfully; but then I had another that all I did was close and reopen it, and then it rendered properly.  The only thing I can think of between the two of them is that both times what I did cleared the ram preview... though that doesn't seem like it should affect it.

             

            - wb

            • 3. Re: blank frames alpha exporting as black
              Mylenium Most Valuable Participant

              Mmh, you could use some trick to enforce transparency - place a graphic at the blank frames that has e.g. only a single visible pixel in one of the corners (and for all intents and purposes, that can be 0.1% opacity even). Nobody would notice... I agree, though, if it sporadically does not render correctly, something is up. Still, I would also look into your playback method. Live mixing systems are quite touchy about timecode and frame sync issues. If there is even only a minor mismatch, they may do wrong transparency keying.

               

              Mylenium

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              • 4. Re: blank frames alpha exporting as black
                westonwoodbury Level 1

                Mylenium,

                 

                Thanks for the notes!

                 

                I thought about doing the pixel idea as well, but haven't had to actually do it yet.  Maybe if it keeps it up I'll look into it.

                 

                As far as playback, this is how it's done on several of the larger TV shows I've worked.  It's similar on both the Fast Forward which is connected to the video mixer/switcher, and the Lyric/Duet graphics system; you bring your movie or image sequence in, and set keyframes accordingly for it to stop at.  For example, on a score bar graphic, one at the beginning on blank frame, one in the middle so it stops once animated in, etc.

                 

                I don't know for sure but I assume they're genlocked when played back for frame sync.  Always seems to looks fine .

                 

                - wb

                • 5. Re: blank frames alpha exporting as black
                  Mylenium Most Valuable Participant

                  I don't know for sure but I assume they're genlocked

                   

                  They better are! One more thought: You might try and use a longer blank area. Most of these systems have a configurable pre-roll, so this should not be an issue. On the assumption, that more frames might avoid encoding/ compression specific issues with wrong headers and such by providing a longer lead in/ lead out, this may also avoid the issue.

                   

                  Mylenium

                  1 person found this helpful
                  • 6. Re: blank frames alpha exporting as black
                    westonwoodbury Level 1

                    Yeah I'll continue to play with AE.

                     

                    Pre-roll being built in makes sense. Guess I've never seen it used though, if the equipment does have it.  Finding out would require busting out the 700 page manuals .  The nature of broadcast work is very 'whatever worked last time' so it's tough, and it seems reliable.

                     

                    Thanks!

                     

                    - wb