Audio drift at DVinfo.net

Arthur Woodle · October 20th, 2008, 10:58 AM

I searched back and could not find the exact fix for my problem. If it has been addressed before, sorry for bringing it up again. I have a client who taped a corporate event which consisted mainly of speakers talking on stage. I don't know what he used to film with, but I do know it recorded straight to hard drive. Something went wrong with his video shoot and he had to scramble to restore all his files. He managed to get all of the pieces and dumped them onto a large external drive. Here is where my problem starts,..he wants me to put it all back together but all the audio drifts out of sync with the video. And on two of the main speaker clips the audio was provided as separate WAV files 44.1 KHz. I converted the WAV files to 48.0 KHz and re-imported to FCP. I thought I could just eyeball the video and audio and do a nudge here and there to keep it in sync, but it is not working, I hate to call the client and tell him I can't do it, ....is there a fix that I can do. I'm not a FCP expert, but I have worked off and on for several years now. Thanks all!

Dave Blackhurst · October 20th, 2008, 12:20 PM

Not sure if I understand the post entirely and I'm a Vegas user rather than FCP, but lets take a wild stab at it...

If I read right, the audio clips are of slightly different length than the video clips, meaning at some point the two were separated and rendered or saved in different formats (likely by whatever program was used to record to HDD), but from the same source camera? This would mean that the content was recorded at the exact same time, but due to format discrepancies the Audio and Video files are not the same length time wise...

You are likely dealing not with "drift" per se, which implies a variable rate of time distortion, but rather a fixed rate of time dilation over the length of the clip, and this is where you should be able to save the ol' bacon...

Line up the beginnings of the related audio and video clips, then look at the ends - if they don't match, change the length of the clip by whatever method your NLE allows that lengthens or shortens the time duration of the clip WITHOUT altering its actual content (in Vegas you use ctrl+drag IIRC). I think I'd choose the audio, but you could also try the video... If you line up the ends of the audio and video of each clip, you should find the entire clip now is "in sync", without a bunch of bump and nudge. Tedious if you've got lots of clips, but should yield good results, and far faster than trying to tweak tiny bits of A/V...

I just used this myself on a file I had to piece together when I couldn't get a particular project to render in one piece in 24p, and when I brought the pieces together there was a significant discrepancy in the audio and video... and I use the same trick to stretch a short video segment to get quick and easy slo-mo to fill gaps!

Hope that provides enough for you to fix the mess you were handed!

October 20th, 2008, 10:58 AM	#1
Arthur Woodle Regular Crew Join Date: Apr 2008 Location: Marietta, GA Posts: 32	Audio drift I searched back and could not find the exact fix for my problem. If it has been addressed before, sorry for bringing it up again. I have a client who taped a corporate event which consisted mainly of speakers talking on stage. I don't know what he used to film with, but I do know it recorded straight to hard drive. Something went wrong with his video shoot and he had to scramble to restore all his files. He managed to get all of the pieces and dumped them onto a large external drive. Here is where my problem starts,..he wants me to put it all back together but all the audio drifts out of sync with the video. And on two of the main speaker clips the audio was provided as separate WAV files 44.1 KHz. I converted the WAV files to 48.0 KHz and re-imported to FCP. I thought I could just eyeball the video and audio and do a nudge here and there to keep it in sync, but it is not working, I hate to call the client and tell him I can't do it, ....is there a fix that I can do. I'm not a FCP expert, but I have worked off and on for several years now. Thanks all!

October 20th, 2008, 12:20 PM	#2
Dave Blackhurst Inner Circle Join Date: Feb 2007 Location: Apple Valley CA Posts: 4,874	Not sure if I understand the post entirely and I'm a Vegas user rather than FCP, but lets take a wild stab at it... If I read right, the audio clips are of slightly different length than the video clips, meaning at some point the two were separated and rendered or saved in different formats (likely by whatever program was used to record to HDD), but from the same source camera? This would mean that the content was recorded at the exact same time, but due to format discrepancies the Audio and Video files are not the same length time wise... You are likely dealing not with "drift" per se, which implies a variable rate of time distortion, but rather a fixed rate of time dilation over the length of the clip, and this is where you should be able to save the ol' bacon... Line up the beginnings of the related audio and video clips, then look at the ends - if they don't match, change the length of the clip by whatever method your NLE allows that lengthens or shortens the time duration of the clip WITHOUT altering its actual content (in Vegas you use ctrl+drag IIRC). I think I'd choose the audio, but you could also try the video... If you line up the ends of the audio and video of each clip, you should find the entire clip now is "in sync", without a bunch of bump and nudge. Tedious if you've got lots of clips, but should yield good results, and far faster than trying to tweak tiny bits of A/V... I just used this myself on a file I had to piece together when I couldn't get a particular project to render in one piece in 24p, and when I brought the pieces together there was a significant discrepancy in the audio and video... and I use the same trick to stretch a short video segment to get quick and easy slo-mo to fill gaps! Hope that provides enough for you to fix the mess you were handed!