Time Stretch

FoskeyMedia wrote on 5/4/2015, 11:52 PM
Shot a video of group singing. Have a second audio track recorded on a Dightal Audio recorder. For some reason (let's not worry about why) that audio file is just about 4 second longer. How do I shring the audio file to be the exact same sice (time) as the first. I know there's a TIME STRETCH effect.. but not sure how to make the 2 files match,

Comments

PeterWright wrote on 5/5/2015, 12:14 AM
I've done this many times.

First go through the Digital Audio track and hit markers at regular significant points, e.g..First beat of the bar at the beginning of either each line, or maybe each verse will be ok. To remind yourself what each marker represents you can name it as the word which happens on that beat.

Now mute the digital audio track and listen to the camera audio. When you reach the beat where you put the first marker, hit the Enter button to pause - split the video at that point, move the right hand section of the video event a few seconds to the right (temporarily) and use Ctrl/Drag to take the edge of the left hand section to the marker.

Now drag the right hand section back to the marker and repeat the process, pausing till the whole song is in synch.

Let me know if anything is not clear!

I did this with this clip for my band - the audio is from our CD:



NickHope wrote on 5/5/2015, 12:14 AM
Hold down <CTRL> and drag the end of the event to size it. Use the waveform preview to line it up. Then right click the event, choose "Properties..." and select "Elastique" as the time stretch/pitch shift method. Experiment with the Elastique options. I can't remember which work best.
PeterWright wrote on 5/5/2015, 12:23 AM
I suggested doing it each line, or each verse .... Nick is saying try it with the whole song at once - it can work, but the trouble with doing this is that there may be many points along the way which do not synch perfectly, that's why I do it in small sections at a time.
TheHappyFriar wrote on 5/5/2015, 5:49 AM
I'd sync up the start & then use the CTRL+Drag method first. If it doesn't match up like it should then I'd do it manually, but I'd find out why it's that far off. Digitial recorders (video and audio) might not necessarily always match up but they shouldn't be 4 seconds off in recording time.
Chienworks wrote on 5/5/2015, 5:54 AM
Ctrl-Drag always works for me, and is always spot-on. While the different recorders might not all be the same speed i've never encountered one that wasn't a consistent speed throughout it's own recording.

Make sure you set the pitch change option to be 'lock to stretch' so the pitch is adjusted to match as well. Any option to 'maintain pitch' is wrong.
dxdy wrote on 5/5/2015, 6:20 AM
The last time this came up, it turned out the OP had one day's video performance, and another day's audio.

Regardless, the methods described here work well.
TheHappyFriar wrote on 5/5/2015, 11:11 AM
Any option to 'maintain pitch' is wrong.

Depends on how hard in the balls hit you want the subject to sound like. :)
FoskeyMedia wrote on 5/5/2015, 11:12 AM
INTERESTING,,,,,
I was going to try the time stretch effect (which I couldn't figure out and now realize i not efficient for this purpose)..But almost unanimously everyone seems to be recommending cntl drag...which I had read about but hadn't tried before or thought abou.t.but makes a lot of sense When I get to my system tonight I'll give it a whirl....THANKS!!!

As for WHY it happened....I don't know and because of time and energy...it's just not worth figuring out at the time (usually I'm more interest in finding the cause than fixing the problem.. I'm getting better).


I will say this....it's weird... There were 4 songs in the set. All of the others were fine except this one..and to be off y 4 seconds for a 5:04 song does seem like a lot. Both the camera audio and digital audio tracks were recorded without interruption. Intriguing. If someone knows the answer or can speculate feel free...but I can't put a whole lot of time into chasing this 'ghost' right now.

Thanks again guys~
johnmeyer wrote on 5/5/2015, 1:33 PM
Make sure that "Elastique" is selected for the stretch method. Do the Ctrl-Drag first, and then right-click on the event and you'll find the setting. The elastique technology is night & day better than the older method; the differences are not subtle or small.
richard-amirault wrote on 5/5/2015, 7:32 PM
Why not leave the audio file alone, and stretch (slow) the video file?

That way the audio will be perfect pitch.
FoskeyMedia wrote on 5/5/2015, 10:21 PM
hmm I think I'll try both. Depends on which gets more distorted and how it effects the track. At first I thought it was a bad idea...actually....the song is "My Funny Valentine"... and old jazz standard.. and I've given it a hazy..black and whiite effect.. so slowing it down may be interesting...even fitting.
Chienworks wrote on 5/5/2015, 10:29 PM
"Why not leave the audio file alone, and stretch (slow) the video file? That way the audio will be perfect pitch."

How do you know that? I would think it much more likely that the video is extremely close to the right speed, while audio recorders tend to have more drift.
NickHope wrote on 5/6/2015, 12:49 AM
Could it be something daft like a 48KHz file being interpreted as 44.1KHz, or vice versa? Although I guess that would show a bigger difference than 4 secs if the track is longer than about 50 secs.
johnmeyer wrote on 5/6/2015, 11:10 AM
You definitely want to change the audio speed, not the video speed. Changing the video speed will:

1. Degrade the video by producing duplicate frame or inventing new frames by blending adjacent frames, or will drop frames. Not good.

2. Speed changes in video are "granular," meaning that speed can only be changed by adding or deleting an entire field or frame. By contrast, audio can be changed by any infentesimal amount.

3. If you choose "Elastique," as I recommended, I defy you to be able to hear any artifacts whatsoever if your speed changes are only 1-2%.