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danielp58171220
danielp58171220
Participant
May 15, 2018
Answered

Converting 30fps to 25fps and preventing Audio sync slipping

  • May 15, 2018
  • 3 replies
  • 25250 views

Hi,

I am helping out a friend who recorded an incorrect frame rate during a shoot involving interviews. The camera used was the Blackmagic Ursa Mini.

The first interview was shot in 30fps in offset mode

The DOP then changed the frame rate to 25fps but offset mode was still on.

The audio is recorded at 48 Hz.

The media needs to be delivered in 25fps.

The first interview is completely out of sync.

The rest slowly drift out if sync after, roughly 15mins on average.

I thought doing a frame rate conversion with the vision would fix the issue, but it didn't work. Any advice/tips?

Danijo

      This topic has been closed for replies.
      Correct answer Richard M Knight

      It seems on BM cameras if the off speed is turned on, even if the camera and sequence framerate are the same, the audio will drift. I would time stretch the audio using sync points at the front and tail of the interview. For the 30fps clip change the framerate of the clip to 30 instead of 25 and then put that into a 25fps Premiere sequence.

      3 replies

      PGZ@Mobibase
      PGZ@Mobibase
      Inspiring
      May 15, 2018

      Try this :

      1) Convert your 30fps media in mediaencoder to output audio only aiff48khz

      2) create timeline in PR using desired output settings at 25fps

      3) import all your media, both 25 and 30fps + newly created aiff audio

      4) when dragging your 30fps to timeline, keep the timeline settings at 25pfs

      5) align / sync newly created audio with your 30fps footage (now playing at 25fps)

      6) disable audio from the 30fps video file and use the aiff audio instead.

      Hope i'm clear....

      danielp58171220
      danielp58171220Author
      Participant
      May 17, 2018

      Thank you, this made sense but speed ramping worked better, as the BM project frame rate was in 25 so the issue was a bit more complicated!

      R
      Community Expert
      Richard M KnightCommunity ExpertCorrect answer
      Community Expert
      May 15, 2018

      It seems on BM cameras if the off speed is turned on, even if the camera and sequence framerate are the same, the audio will drift. I would time stretch the audio using sync points at the front and tail of the interview. For the 30fps clip change the framerate of the clip to 30 instead of 25 and then put that into a 25fps Premiere sequence.

        danielp58171220
        danielp58171220Author
        Participant
        May 17, 2018

        Thank you! That worked well. If you're watching for it, it's not perfect but it's definitely useable. Cheers!

        Danijo

        E
        excited_Genie16B8
        Legend
        May 15, 2018

        What's offset mode?

        danielp58171220
        danielp58171220Author
        Participant
        May 15, 2018

        Apologies, I now have further information. It was the 'off speed frame rate' of the Ursa Mini. So the Project Frame rate was 25fps however the Off Speed frame rate was 30fps for the first interview, then 25fps for the rest (but was still switched on) so for some reason the audio drifts. It may be to do with audio sample rate, but wanting to eliminate any visual issues first.

        E
        excited_Genie16B8
        Legend
        May 15, 2018

        Your camera op essentially recorded the first interview in slow motion mode, where audio is generally not used.

        You might be hosed.

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