Lags between audio and video

Alberto Rojas

Freshman
Jan 3, 2015
4
0
1
36
Hello,

I am trying to mix the video and the audio of a piano performance.

The audio was recorded with a VST and the video was recorded with a smartphone at 30 FPS.

When I mix them, I make sure the audio and the sound start sincronized and the first part of the video is pretty good but with the progress of the song some lags start to ocurr: sometimes the video is delayed and sometimes (specially when im playing faster) the audio is delayed.

This is the first time I am doing this and I have not been able to find much information on the web, specifically for this problem I am having.

The sound was recorded at 120 Beats per Measure and the Time Signature was 4/4.

The softwares Im using are:

Pianissimo (by acoustica) for the piano.
Openshot to mix the video and the sound.

Is there something I could do to fix this?

Could this be a hardware issue?

Thank you very much for your advice.

Best regards.
 

Ben Lawrence

Senior
Mar 2, 2011
1,083
20
38
Vermont
vtaudiovisual.com
Check that you have the same sample rate in your file and project. IE:44.1k-48k. I have dealt with this a bit in a few projects. The drift took long enough that I just cut the audio file and slid it back a bit periodically to line it up. Probably not the correct way but it got the project done. You should be able to line up the waveforms without too much issue.
 

Simon Eves

Sophomore
May 12, 2013
189
0
16
With respect to Ben, a 44.1/48 sample rate difference is going to be VERY obvious, as that's nearly a 10% difference which is a couple of semitones of tuning and it would drift very quickly and obviously. Consumer gear just sometimes doesn't have very accurate clocking, and two devices can just drift.

My fix for this has always been to sync the audio and video at one end, measure the drift at the other end, and compute the speed-up (or slow-down factor) to process the audio (most easily using the Change Speed operation in Audacity) to match. For example, if the recording is two minutes long, and the sound is 0.5s ahead of the video by the end, then it needs to be slowed down by 119.5/120 or 99.5833%. Conversely, if it's 0.5s behind, it needs to be sped up by 120.5/120 or 100.4166%.

The other possible reason is that the 30fps may actually be 29.97fps (US NTSC TV frame rate) and one device or the other, or perhaps your editing software, may be compensating for this and causing a 0.1% drift.