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High Speed Frame Rates


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Hey Everybody, 

Technical question: I’ve been asked to provide ProTools music playback for a video that will be filmed at high speed (47.952 fps) and then ultimately played back (or shown on TV) at 23.976 fps.

To achieve this. the talent will be lip syncing with the 2x music, so that when it’s slowed down the lip movement will appear normal.

My question is this: Is there any way for me to be sending timecode to the Location Sound Mixer as we are filming? ProTools doesn’t offer fps of anything higher than 30, and nor does the Location Sound Mixer’s recorder.


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This has been done before. (Mostly on music video clips.)


You can use AUX tc (record the LTC on a spare track.) This is a great way to have multiple angles fall in place by itself, no need to do the entire track for just a 2 second shot. Do allow for enough preroll to give the talent time to get up to pace / in the rythm.)

If you have direct out, why not generate an LTC stream and speed it up as well? (Without pitch correction, as you probably do on the sound track!)

LTC was designed to be readable at very high speeds (while searching tape).

At 48Khz, a 23.976 bit is  about 25 samples. (48000  / 23.976 / 80  (there are 80 bits in one frame).

Now, a bit needs two samples at least, so in theory you could speed it up 12 times.


If you can't generate LTC yourself and you don't want to record it, get my LTCconvert demo, it comes with 10 minutes of LTC in all framerates.



If you need a lot / custom start / duration, you can use my LTC generator.


(This thing will generate 24 hours of LTC as BWF within minutes.)


I could customize it to run other speeds, but if you're handy with a HEX editor, you can easily alter the sample rate to 96000 so it runs twice as fast. Goes for the prefab files as well of course.


The only tricky part is that you have to tell post to slow down the sound as well, without pitch correction, and actually use the AUX.



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  • 2 weeks later...


The sped up and slowed down music will obviously not be used in the video, it will be replaced..

So the production person records the sped up audio back to the camera.

During video post the music get pulled down to 23.976, along with video, and post audio replaces the music.


Same concept when using film in the 90s, music was played back at 48.048k, telecine pulled it down to video, and post audio would sync the original music back om.

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