5 Replies Latest reply on Mar 3, 2011 8:31 AM by the_wine_snob

    How / Why is audio being truncated

    dorich24 Level 1

      Basic Problem:  All the audio on imported video clips is being cut off after approximately 7 secs.

       

      Description:

      I have a set of clips that were made on a Nikon Coolpix. They were imported firstly into iMovie where they played correctly. Then I imported the same clips into PRE.

      I moved a couple of clips onto the timeline where they appeared to play correctly.

       

      I started experimenting with a narration track, the narration coming from a USB mic.

       

      I now find that the audio on the video tracks is truncated after about 7 secs, in other words the sound starts playing and then stops at about the 7 sec mark.

      If I detach the audio from the video and look at the waveform you can see the first 7 secs as an expected sound waveform and then the display changes to a rectangular box with no sound waves. I tried to capture an image of the waveform, or lack of it but it appears that the waveform view is on the same level as the screen capture process so I can't capture the image.

       

      All of the clips seem to be suffering from this problem suggesting that I must have changed something at the macro level to create this problem but I'm at a loss to know what would effect it.

       

       

      I'd appreciate any pointers as to what might be the source of the problem and how I might correct it.

       

      Thanks.

       

      Background:

      OS X 10.5.8

      PRE 9.0.1

        • 1. Re: How / Why is audio being truncated
          the_wine_snob Level 9

          Did you let the Conforming of your Audio to complete 100%? That is the main reason for truncated Audio - one begins editing, before Conforming completes. This ARTICLE will give you background.

           

          Good luck,

           

          Hunt

          • 2. Re: How / Why is audio being truncated
            dorich24 Level 1

            @ Bill Hunt

             

            Hi Bill:

             

            Thanks for the feedback.

             

            After some trials I believe the "conforming audio" is not the problem (or maybe it is and I don' understand it). After importing a clip there is no indication that there is any processing going on - also there is a small 'P' in the lower right hand for the thumbnail. I can't find any explanation of what the letter 'P' means.

             

            I removed all the offending clips and tried reimporting them but still ran into the same problem, even tried importing and letting it sit for an hour to make sure there was no processing going on that I couldn't detect - overkill I know.  Didn't solve the problem.

             

            I tried cleaning up the media cache via the preferences menu, after I deleted the offending files. Then reimported but to no avail.

             

            I erased the project and all related files and repeated the whole process but still would not work.

             

             

             

            What did work

             

            I tried importing an older file from a different event, also a file from the Nikon, and found that it suffered the same problem.

             

            So I converted the file to mpeg4, imported the converted file and it worked perfectly - the quality of the video appears somewhat degraded but the audio is complete.

             

            I repeated this with a different process. Made the clip into a project in iMovie, exported it and then imported that file into PRE. It worked just fine.

             

            Now I notice that sometimes when I import a file that come from the Nikon PRE asks me if I want to fix the quality.

             

            So, in my naivety I'm guessing that this problem has something to do with the quality of the clip.  I don't know much about these things but I understand that the extension mov could mask a variety of formats and so perhaps there is something that PRE can't digest very well in the file exported from the Nikon.

             

             

            Thanks for the reference links, very much appreciated.

            • 3. Re: How / Why is audio being truncated
              the_wine_snob Level 9

              Interesting observations.

               

              Going back to Conforming, there is a little progress bar at the very bottom-right of the GUI, that shows the progress of the Conforming. PrE must Conform the Audio stream to 32-bit, floating point for accurate editing. The closer the Audio is to 48KHz 16-bit PCM/WAV, the shorter the Conforming time will be, and might go by so quickly, that one would miss it. The Duration of the Clip also plays a role in how long this progress bar will display. On a short, 48KHz 16-bit PCM/WAV Audio stream, it will be in the blink of an eye. For, say 32KHz 12-bit Audio, and a long Clip, it might take a minute, or more to Conform. I recommend not even touching the computer, while Conforming is going on, and to definitely NOT drag any Clip to the Timeline, while Conforming is in progress. One should just be patient.

               

              Now, Adobe programs have issues with some MPEG Audio, whether muxed (Multiplexed into a single file with both an Audio and Video stream), or even just an Audio stream, like an MP3. MPEG Audio can just be problematic, and the issues can manifest themselves in various ways.

               

              When dealing with MPEG Audio, I always convert to 48KHz 16-bit PCM/WAV, outside the program. If muxed, then I rip the Audio from that combined file, convert it and Import it separately. If an elemental stream, say an MP3, then I just convert before Import. I use Adobe Audition, but the free audio-editor, Audacity, will do this too, and do it well.

               

              Many Nikons use the MJPEG CODEC for motion, and I believe with MPEG Audio. Though I have a handful of Nikons, I have to admit that I have never used any for motion capture, plus my units are rather old by today's standards, so even a test might not apply with newer Nikons. Were I faced with MPEG Audio, I would rip, and then convert everything to PCM/WAV 48KHz 16-bit, and be done with it.

               

              Good luck, and hope that you have found the key to editing the material. Does your Nikon use the MJPEG CODEC, regardless of what the format "wrapper" is? What is the CODEC used for the Audio stream in those muxed files? Just curious.

               

              Hunt

              • 4. Re: How / Why is audio being truncated
                dorich24 Level 1

                the_wine_snob wrote:

                 

                Interesting observations.

                 

                Going back to Conforming, there is a little progress bar at the very bottom-right of the GUI, that shows the progress of the Conforming.

                Thanks, now I know what to look for.

                 

                 

                When dealing with MPEG Audio, I always convert to 48KHz 16-bit PCM/WAV, outside the program. If muxed, then I rip the Audio from that combined file, convert it and Import it separately. If an elemental stream, say an MP3, then I just convert before Import. I use Adobe Audition, but the free audio-editor, Audacity, will do this too, and do it well.

                I assume that once its imported the conforming process "sync's" the audio with the video?

                 

                Many Nikons use the MJPEG CODEC for motion, and I believe with MPEG Audio. Though I have a handful of Nikons, I have to admit that I have never used any for motion capture, plus my units are rather old by today's standards, so even a test might not apply with newer Nikons. Were I faced with MPEG Audio, I would rip, and then convert everything to PCM/WAV 48KHz 16-bit, and be done with it.

                Good luck, and hope that you have found the key to editing the material. Does your Nikon use the MJPEG CODEC, regardless of what the format "wrapper" is? What is the CODEC used for the Audio stream in those muxed files? Just curious.

                My unit is relatively old. Its an L1, circa probably 2005. I've searched around but can't find any specification on the CODEC used.

                I'll work on the audio export process

                Thanks for all your help, very helpful as always and greatly appreciated.

                • 5. Re: How / Why is audio being truncated
                  the_wine_snob Level 9
                  I assume that once its imported the conforming process "sync's" the audio with the video?

                   

                  In most cases, after Conforming, there is no loss of sync.

                   

                  Now, some of that can depend on the specs. of the original Audio stream. When there is OOS, it is usually because the original Audio stream used some form of MPEG CODEC. Those can, and often do, cause issues. One of the reasons is that the block size for MPEG Audio is different than for Video. In short Clips, this is never noticed, but with very long Clips, can manifest itself as dynamic OOS.

                   

                  If one does encounter OOS, whether static, or dynamic, this ARTICLE might be useful.

                   

                  Good luck,

                   

                  Hunt