Blackmagic Forum

So I shot a scene at 50fps slowmo for 25fps timeline - that is, the video playback is 50/25 so it plays slow in-camera.

Ok seems normal.

Then I realize, that I need to sync the audio. Of course, 50fps is exactly 2 times as much as 25fps, so one would think, that just speeding up the video twice (to 200% in Premiere) will match exactly with the audio that is 25fps anyway.

Wrong.

The audio always comes a bit shorter, like a few frames, or more than a second, for longer takes. Any thoughts?

P.S.
Pocket 4K, Prores 422

You won't get proportionally sync sound with off-speed frames rates, even when the off-speed rate is the same as the project rate. The manual makes this clear. Off-speed is for picture only.

I understand that, but I cant get the mathematics.

If the audio records at 25fps and the picture records at 50fps, why would not speeding up the picture by 200% get it in sync?

Sp the audio does not record at 25fps at off-speed rates. The difference in the timeline is so small, you can almost match it, but not quite perfect.

Try 24 fps.
If this coincide exactly, the audio was recording at 24 and is a bug.

Emilian Dechev wrote:I understand that, but I cant get the mathematics.

If the audio records at 25fps and the picture records at 50fps, why would not speeding up the picture by 200% get it in sync?

Sp the audio does not record at 25fps at off-speed rates. The difference in the timeline is so small, you can almost match it, but not quite perfect.

In off speed the video and audio are not running from the same clock, so they will drift. It may be close, but the longer the clip the more it will likely drift.

I have found - after trying to import footage for a multicam shoot, that the audio always seems to record in 24fps where the video was recorded in 50fps. I also tried to change to 25fps to match the audio as I thought it matched my non high speed mode footage and found that the video still fell a bit short on the audio track. But then found that running my clip settings frame rate as 24fps it matched the audio correctly. From there I just exported it in the best format I could as 25fps so that it matched my other multi cam files when I synced them up.

I am sure there is a much better way to get around this... But the issue is so hard to explain that it is very difficult to get any clear answers or direction.

I just make sure that when im on multicam shoots that I don't have the high framerate button selected :/
Definitely going to keep an eye on this thread to see If anyone has a better solution for correctly interpreting off speed footage so that the audio matches.

Generally running off-speed in a multicam situation is unwise.

The simple solution is to shoot 50fps native, this will keep sync audio.