Why Blackmagic movie audio half the length of video?

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Mark Palmer

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Why Blackmagic movie audio half the length of video?

PostWed May 12, 2021 3:28 am

Movie recorded on Blackmagic 6K has audio that is about half the length of video (a little more, like 3/5). The audio just cuts off while the video plays on. Why and how to fix? Audio is correct speed, video too slow.

30fps ProRes 422
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rNeil H

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Re: Why Blackmagic movie audio half the length of video?

PostWed May 12, 2021 3:39 am

That means the camera was set for high speed to create slo-mo. There's a switch on it to go between normal speed and slo-mo. Which of course is done by recording more frames per second than the set for.

Then plays back at normal fps with smooth slo-mo.

But yes, the audio is only have as long as the video.

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Mark Palmer

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Re: Why Blackmagic movie audio half the length of video?

PostWed May 12, 2021 3:43 am

Ok, thanks. I didn't realize it was set to slo-mo. I assume all I have to do to fix is speed it up 2x.
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antoine

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Re: Why Blackmagic movie audio half the length of video?

PostWed May 12, 2021 5:44 pm

Speed the video yes, but try not to speed up the audio track at the same time !
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Mark Palmer

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Re: Why Blackmagic movie audio half the length of video?

PostWed May 12, 2021 5:51 pm

Yes, got it! I also found that I accidentally slowed it down from 30fps to 50fps, so speeding it back up to normal was giving me problems until I realized it wasn't simply 2X but 5/3! What's the point of not making it an even 2X? Weird.
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carlomacchiavello

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Re: Why Blackmagic movie audio half the length of video?

PostFri May 14, 2021 6:50 am

Mark Palmer wrote:Yes, got it! I also found that I accidentally slowed it down from 30fps to 50fps, so speeding it back up to normal was giving me problems until I realized it wasn't simply 2X but 5/3! What's the point of not making it an even 2X? Weird.

it's not weird, when you choose to do a slow motion camera allow you to slow as much as possible, if you go to fhd you can up frame rate to 120 fps to do a better slowmotion, but audio are captured at normal speed.
every bmc can do slowmotion and timelapse directly in camera changing project and playback setup, when you change it you can do these kind of effects in camera. Sometimes happen that you click HFR button in the rear of camera and enable it. To avoid mistake during high pressure work you can setup hfr at same speed of normal shooting, that mean also if you hit accidentally the HFR button, you shoot at same speed.
To avoid change of speed and to avoid filling space more than common shooting.

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