Audio / video sync issue for music video

Neel wrote on 8/21/2020, 9:54 PM

I'm working on a music video project that is 21 minutes long - basically the entire EP.

The music was exported as a 32-bit WAV file, 44.1 kHz.

The video was recorded at 23.976 fps while lip-syncing to the mp3 playback from an iPod and portable speaker. The shutter speed of the camera was 1/50 sec. The camera is a Panasonic Lumix G85 and I recorded the video in 4K.

I synced up the beginning, but as the video progresses, the video is drifting earlier. By the end of the video, it's very noticeably out-of-sync.

There is other footage being edited in, so I tried nudging later clips of the singer over to try and sync them to the audio, but it's not perfect.

There is an opportunity to re-record the video. Is there a specific frame rate I should be shooting at to avoid this sync issue? There's no discrepancy between the WAV file and the mp3.

Is this enough information to say what frame rate is best to be shooting at? Is it possible and maybe better to connect the camera via USB to the computer and record directly to VMS?

Thanks

Neel

Comments

Musicvid wrote on 8/21/2020, 10:07 PM

The camera clock and the playback clock and recording clock are not all synced by an XLR cable carrying freerun SMPTE plus Genlock, so yes, they will drift. Something like an h4N will get you a lot closer, but not frequency-perfect. Your question does not relate to video frame rate.

Former user wrote on 8/22/2020, 8:03 AM

As a test, try recording the music to your camera via a cable (or mic if no line input) using the same audio playback device that was used in the original shoot. Put both on a timeline and see if they hold sync. As Musicvid says, if they aren't locked by a sync generator, there is a chance they will drift apart. Some devices are more accurate than others. Doing a reshoot with the same equipment will probably not improve the situation.

Neel wrote on 8/22/2020, 11:58 AM

Thanks guys, I did a test by starting to playback the audio on my iPod and in VMS at the same time. At first it was like a slight offset delay, but towards the end of the 21 minutes, it noticeably drifted. Conclusion: the iPod plays back slightly faster, which doesn't matter for a 4-min song as much, but over 21 minutes, it don't work.

I've never used SMTPE before, and pretty sure my camera doesn't even support it. I'm really a passionate amateur hobbyist at this stuff.

I tried a test video using VMS for the playback reference instead of the iPod, and it worked perfectly - everything is in sync. Now I just have to setup the proper video shoot again.

Neel

Musicvid wrote on 8/22/2020, 12:50 PM

You should be able to fix this in two steps. Split your "faster" audio track approximately in the center, at a quiet spot at exactly zero-waveform crossing. Then align the segment waveform peaks near their centers with your master track. This is better to me than introducing Q-Noise by stretching the tracks.

This is what a zero-crossing waveform looks like on your audio track:

Neel wrote on 8/22/2020, 2:45 PM

Thanks Musicvid,

I have a lot more experience with audio editing and I know about zero-crossing waveforms. However, for this video, the audio from the camera is only used to sync the video with the studio recording of the songs, then it is muted.

I think the best thing for me (and actually not too difficult) is to re-record the video and have an easier time editing.

Neel

Musicvid wrote on 8/22/2020, 3:18 PM

However, for this video, the audio from the camera is only used to sync the video with the studio recording of the songs, then it is muted.

That's how I did it for over a decade of full-tilt event productions, Neel.

Pluraleyes helps, a lot.