Saturday, July 03, 2010

The speed of sound

A friend is editing a video he took of a stage performance, and I recommended the utility PlurtalEyes for syncing the different video clips. PluralEyes is a software program that will take video and audio files and match them based on the audio tracks.

He downloaded the beta of the Premiere Pro version - after having trouble finding it because he thought I was talking about a tool called Pluralize - and found it did a pretty good job of matching the tracks, but he felt it was perhaps a frame or two off in some cases.

It was only after talking about it for a while that it occurred to us that the speed of sound might be coming into play; he has one camera set-up on the stage, and two set up at the back of the auditorium. He reckoned it was about 100 feet from the front of the stage to the back of the hall.

A quick search turned up the speed of sound in feet per second: 1,125.

Which translates to: 37.5 ft every 1/30 second.

Which means that the audio could be two or three frames out! (he reckons two frames.)

Remember that next time someone says you don't need middle school science to succeed!

Singular Software: PluralEyes

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