10 Replies Latest reply: Nov 25, 2012 7:51 PM by J. Simon RSS

    Why would an audio track cause a video glitch?

    joneisele Community Member

      I have a 1080 60p clip with no audio.  If I create a sequence based on that clip, add a wav file to an audio track, then export using the H.264 60p custom preset with audio multiplexing to an .m2t everything looks fine.    However, if I export using the H.264 Blu-ray preset, 720p, 59.94, multiplexed, to an .m2t file the video has some stutters towards the end.   If I remove the audio track and do the same export, still muxed, the video is fine in 720p.   I get the same result if I start with a 720p sequence (i.e. addition of audio causes video glitch).  

       

      Edit: tried a different audio file, this time .mp3, same problem.

      Edit: importing the muxed 60p export with audio, then exporting as noted in 720p has the same issue.

       

      Comments?   Let me know if what I'm describing isn't clear.

        • 1. Re: Why would an audio track cause a video glitch?
          joneisele Community Member

          Updates: if I export using H.264, 720, 30p, I don't see the issue.  No issues with H.264, 1080, 30p.    If I export using H.264, 720, 59.94 it comes out a lot better than H.264 Blu-ray; I can still detect the issue, but far less noticeable.  

          • 2. Re: Why would an audio track cause a video glitch?
            joneisele Community Member

            More: 1080 30i has the same issue.  1080 24p does not.

            • 3. Re: Why would an audio track cause a video glitch?
              J. Simon Community Member

              What is the end goal here?  DVD?  Blu-ray?  Web?  Computer playback?

              • 4. Re: Why would an audio track cause a video glitch?
                joneisele Community Member

                The end goal is both Blu-ray disc and native file playback on a PS3.   The clip in question is a "movie logo" that would be included with a bunch of 720, 59.94p footage.   Plan to produce a muxed .m2t file that can be burned directly to BD and also play on my PS3 natively (via streaming / DLNA).   However, in the future I will potentially be using 1080 60p footage.   Let me know if you need more information.

                 

                To be clear: it appears I can re-encode the video clip to various formats just fine.  It is only when an audio track is included that certain exports have this glitch.  

                • 5. Re: Why would an audio track cause a video glitch?
                  J. Simon Community Member

                  in the future I will potentially be using 1080 60p footage.

                   

                  You can't put that onto Blu-ray as-is, so there's little sense in shooting that way for anything but planned slow-motion shots.

                   

                  At 1080, your frame rate options will be 30i or 24p.

                   

                  At 720, your frame rate options will be 24p or 60p.

                   

                  Plan your shoot with that in mind (and possibly reshoot the current stuff).

                  • 6. Re: Why would an audio track cause a video glitch?
                    joneisele Community Member

                    Understood on BD not supporting 1080 60p.   My plan was to use downscale the movie logo to 720p for now.  That in theory shouldn't be a problem.  Ignoring the use case though ...

                     

                    My question was why a 1080 60p video clip exports to 720p 59.94fps just fine unless an audio track is included.   Odd, but with audio 1080 30p and 24p come out ok, 720 30p is ok, but not 1080 30i.  

                     

                    I tried another experiment: I exported the video clip only from 1080 60p to 720 59.94.  Then imported the .m4v file into a 720p 59.94 sequence, added an audio track, exported, same problem ...

                     

                    Thoughts?

                    • 7. Re: Why would an audio track cause a video glitch?
                      J. Simon Community Member

                      Ignoring the use case though ...

                       

                      There's no point in clearing a downed tree if the road you're on is a dead end.  Best to use that time to backtrack and get yourself on the right road.  If that tree is big enough to cover both roads, then you can worry about clearing it.

                       

                      So, start off on the right road.  Match your footage and sequence to the desired Blu-ray output.

                      • 8. Re: Why would an audio track cause a video glitch?
                        joneisele Community Member

                        Hi Jim - understood in an ideal world one would have source video footage, sequence, and output target all the same.  Is it not common though for folks to have situations where there is more than one target output?

                         

                        Anyway, I think I have a tree covering both roads if I understand your analogy.  What is wrong with the following picture?  I took the original 1080 60p clip, dragged it into a 720p 59.94 sequence, exported the video only.  The exported video looks just fine in this case.  I even tried different formats (Matrox MPEG I-Frame HD, H.264 Blu-ray muxed and not).  It is all good.

                         

                        Next I imported the aformentioned no issue video that is in 720 59.94 into a sequence that matches then exported to a matching format.   No issue with the resultant video.   Is this scenario not what you mentioned?   Start with video that matches the sequence and target output?   

                         

                        However, if I add an audio track, the video has some flashing/stuttering at the end particularly towards the top.   Why would exporting with or without an audio track in the above scenario make a difference?

                         

                        In case it matters, the video came from a modified After Effects template.  I don't own AE and paid another guy to modify the template.  I will go back and ask him to render in 720p 59.94.  Still, the above just doesn't seem right. 

                        • 9. Re: Why would an audio track cause a video glitch?
                          joneisele Community Member

                          More data: I have been selecting VBR, 2-pass.   If I leave as VBR, 1-pass the issue goes away.  

                           

                          To summarize, starting with the original 1080 60p clip or rendering that clip to 720p 59.94fps and re-importing; creating a new sequence that matches, then exporting with H.264 Blu-ray four files as follows:

                           

                          Video only, VBR 1-pass: OK

                          Video only, VBR-2 pass: OK

                          Video + audio, VBR 1-pass: OK

                          Video + audio, VBR 2-pass: stuttering/flashing towards the end.

                          • 10. Re: Why would an audio track cause a video glitch?
                            J. Simon Community Member

                            That is weird.  But no one is likely to notice any different between 1 and 2 passes, so I'd say go ahead and use 1 pass.