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Re: Exported audio sync issue

  •  03-18-2020, 18:52

    Re: Exported audio sync issue

    I've now done some tests here using PS23.1.1.242 Ultimate...

    A/V sync problem occurs with both NTSC and PAL - but here is far worse with NTSC; in a 5 minute test project the error was 0.56 seconds for PAL and 0.92 seconds for NTSC (in both cases the audio "gets ahead" of the video. And I can now see that the reason why I did not observe the errors in my other recent projects is that the edits were short passages trimmed from the MTS source files and linked together by crossfade transitions (in "Overlap clips" mode). So the A/V sync probably did get "off", but was reset at every transition!

    A recipe that can clearly demonstrate the A/V sync error - apart from Studio it just needs the Audacity sound editor with the FFMPEG plugin installed (so that Audacity can read/import the audio tracks from video files):

    1. Prepare a sound track as a WAV file that contains very distinctive sound cues - here I used Audacity to create a 5 minute WAV file containing "120 beats per minute" metronome ticks. Import that sound file into Studio.

    2. Start a new project and configure timeline settings as Widescreen16x9), Regular (2D), HD 1920x1080, 29.97 (60i) for NTSC

    3. Add the sound file to the project (A/V track 2); on A/V track 1 create a default classic/motion title "Your Text Here" and set duration to exactly cover the entire audio file (e.g. 5 minutes)

    4. Export as a Transport Stream (MTS) file using the preset "HD 1080i"

    5. Import that MTS file into Studio and add to a new project using the same project settings as in step (2) above

    6. Export as MTS, again using the preset "HD 1080i"

    7. Open Audacity and drag the three files into the Audacity propject:
      (a) The original WAV file
      (b) The MTS file exported in step (4) above
      (c) The MTS file exported in step 6 above

    8. Scroll to the end of the Audacity project timeline and zoom in; it will be observed that:
      (a) The original WAV file and audio from the MTS file exported in step (4) stay in sync (here, there is a small, insignificant offset observed between the two audio tracks)
      (b) The audio from the file exported in step (6) "finishes early" and has become noticeably out-of-sync (nearly 1 second in 5 minutes)

    9. Scroll along the Audacity timeline and it will be observed that the audio from the file exported in step (6) appears to "lose frames" at irregular intervals (it starts in sync, but there is not a slow regular drift, the increases in the A/V sync error occur in distinct steps of around 30 milliseconds.


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