16 Replies Latest reply on Sep 13, 2012 2:16 AM by Screenarena

    Random Glitches When Rendering Movie


      Two current jobs I'm working on are displaying strange glitches during the first seconds of the render. These appear for one frame at either the top or bottom of the frame. A render may contain just one glitch or sometimes three or four. The rest of the render seems to be fine. The glitch can appear as a green line or a couple of lines of snow. I have seen a frame slip on one particulalry bad occassion.


      I re-render and sometimes I get away with it, but other times the glitches appear at other random frames, but always near the begining.


      I wondered if this might be a mains spike or something, but why only at the begining (sometimes I leave the studio and switch the light out once a render is underway. That might have provided a spike at the begining of a render. I stopped switching the light out but no difference). I've not had this kind of problem before. Getting a complete render without a glitch has become a bit of a nervous lottery.


      I'm adding three shots. The first are my computer specs. The next two are examples of the kind glitch problems I'm getting.


      Any thoughts?


      Computer Info.jpgglitch example 1.jpgglitch example 2.jpg

        • 1. Re: Random Glitches When Rendering Movie
          Mylenium Most Valuable Participant

          Looks like encoding errors in MPEG footage. Without knowing your settings this is impossible to diagnose. often this happens with VBR encoding, when the analysis is not "stable" in teh first few frames and data rates are less balanced than at later points, where more statistical data is available.



          • 2. Re: Random Glitches When Rendering Movie
            Screenarena Level 1

            Hi Mylenium. Thanks for your thoughts which are probably correct for MPEG encoding, except that in my case I'm rendering a Quick Time YUV 8 bit 4:2:2 1080 x 1920 movie. It doesn't matter whether it's with or without audio.


            • 3. Re: Random Glitches When Rendering Movie
              bogiesan Level 4

              You ahve not mentioned what the source video files are. If they're compressed or encoded at all, try unpacking them to a full frame codec before trying to build your comp.

              Since the effec is random, not repeatable to the frame and pixel, it's either your media or your drive connection from where the media is stored. I'm guessing it's a bad media file.

              • 4. Re: Random Glitches When Rendering Movie
                Screenarena Level 1

                Re the source footage. In the case of one project they are HDV mpg files, in the other project they are Quick time .mxf files In both case they are the original camera rushes.


                The media in both cases is fine having rendered OK when making a test movie from the off -line in PPro. When rendering out in AFX I've tried different drives to render to. It doesn't seem to make a difference to the problem.


                It's the random nature of this problem that is so annoying.


                • 5. Re: Random Glitches When Rendering Movie
                  Mylenium Most Valuable Participant

                  HDV is compressed and MXF is just a container format. That doesn't mean nothing. Unless you can convert the files to QT animatioon or another CoDec, there is no way to surefire verify. Yeah, I'm sure it's annoying, but AE simply works differently and you may need to help it along...



                  • 6. Re: Random Glitches When Rendering Movie
                    Screenarena Level 1

                    Hi Mylenium.

                    Yes, I know that HDV is a compressed format and that .mxf is just the container for a version of Quick Time that would otherwise not import into AFX (or PPro). I've been rendering away happily with AFX for years now but this is an unusual; random problem that has only just appeared.



                    • 7. Re: Random Glitches When Rendering Movie
                      bogiesan Level 4

                      Re-reading the thread, we've been informed the problem clip is compressed and requires unencoding before it can be rendered.That they are original camera footage is irrelevant. That this has never happened before is also irrelevant. Random events are not random at all, they have identifiable causes.  You've eliminated the drive as a likely cause but not the media itself. That's always my first stop. You can easily debug this by turniong off the layer and running a test render. No glitch? Convert the problem clip into a frame-based codec and replace the footage in the comp. If the results are still glitchy, all we have done is eliminated the first, probable, obvious and most likely cause. Then we will suggest you go after another.

                      • 8. Re: Random Glitches When Rendering Movie
                        Screenarena Level 1

                        Well Bogiesan, just to be clear, this  problem currently appears in two different jobs each one using a different footage type. Some times a glitch appears and sometimes it doesn't.  It is random rather than inexplicable. I can't be confident that when I render, glitches wont appear or where they will appear and is therefore random in nature. I am quite certain there is an explanation for it.


                        Actually, I don't think it is the footage, but I do think the elimination process you suggest could be helpful. The only problem of course, if I get a clean render, will it be simply because on that occassion the glitches didn't appear (as they often don't) or as a result of the eliminated layer / effect?


                        This is getting metaphysical!



                        • 9. Re: Random Glitches When Rendering Movie
                          bogiesan Level 4

                          I could draw from my tarot deck and arrive at the same conclusion and it would be equally misled.

                          There are no random events with digital rendering. There are no events that occur within AE that cannot manifest in other applications or in events at the OS level. Computers do not work that way. Corrupt uncompressed files create glitches at exactly the same place every time. Corrupt compressed files cause what appear to be random glitches but the cause — or linked causes — is absolutely identifiable, even if it is not easily locatable. Corrupt codec software is always corrupt and every file using that same codec will present similar glitches.


                          One debugs unusual and unexpected events in After Effects in a logical and binary approach. To do anything else produces results easily misinterpreted by wishful thinking instead of the yes/no branching. If this event occurs in only these two projects, there is something wrong with the projects. Move the footage to another project. Does the glitch follow? It's the media. Does the glitch go away? It's one of the filters applied to the footage item. End of branching.


                          We've told you what we know and explained why your conclusion is probably incorrect.

                          • 10. Re: Random Glitches When Rendering Movie
                            Screenarena Level 1

                            Bogiesan my dear fellow, I feel like I'm being told off! I know I'm probably a very naughty boy but I normally leave that kind of thing to my mother!


                            The footage in one of the projects is in fact an up-dated version of a previous AFX film. It has always been fine. I've just up-dated my SC5.5 software and am waiting to see if that improves things.


                            Watch this space....more news on this channel later!


                            • 11. Re: Random Glitches When Rendering Movie
                              bogiesan Level 4

                              Umm, sorry about that.

                              • 12. Re: Random Glitches When Rendering Movie
                                lasvideo Level 4

                                I have experienced some glitches recently in AE that were alleviated when I turned off multiprocessing.

                                • 13. Re: Random Glitches When Rendering Movie
                                  Screenarena Level 1

                                  That's interesting. Along with other suggestions I'll give that a go.

                                  • 14. Re: Random Glitches When Rendering Movie
                                    Screenarena Level 1

                                    Hey, no worries. I'm a light hearted chap who enjoys his work, even when technical probs get in the way. Mind you, I've had one or two occassions when I wanted to park my edit suite in the garden.....via the window!


                                    • 15. Re: Random Glitches When Rendering Movie

                                      I'm using AE CS6 and I have the exact same problem here. I'm experiencing random glitches here.

                                      I'm exporting in QuickTime format (Animation compression) with or without alpha and all the footage in the composition is generated by AE, no videos or pictures.

                                      An example.

                                      f###ing glitch.jpg


                                      I've tried everything. I can export the same composition 3 times and one has no glitches and two have them in diferent frames,

                                      The problem occurs in my two computers,

                                      • 16. Re: Random Glitches When Rendering Movie
                                        Screenarena Level 1

                                        Well, xxtpam.

                                        I really do feel sorry for you. This kind of thing can drive you mad. While I was very grateful for the suggestions offered by everyone, nothing solved the problem. Until that it is, someone from a  company in the UK that have built  edit suites for me in the past suggested reinstalling the operating system. This is a fairly drastic solution because of the inevitable loss of data and having to re instate everything that might be lost in the reinstall.


                                        For me, it was worth it because it worked. I no longer have the glitch problem on that edit suite. For your info, that company is DVC down in Brighton, Sussex.


                                        I should mention that such was the problem, I got them to build me a new edit suite  and moved everything over to that one. It's a big beast of a machine and about as fast as you can get. The "glitch" machine is now "glitch" free but used only as a secondary resource.