sync audio and video

C

cazint

New member
I came to this site via google, after being linked to the following thread:
http://www.dvxuser.com/V6/showthread.php?t=191176

My situation is similar, but really, on a really basic level.

Most of you, perhaps all of you, are like video gurus (experts) using high end equipment. Unfortunately, this is not the case with me. I have a low-end Panasonic camcorder...it doesn't even allow a mic input. Yes, I know, time for an upgrade! For now, we'll call it the "recession camcorder".

Because of no audio input, I use an Olympus digital recorder to try to get clean audio. Mind you, this is a small time thing for church videos. We're not trying to be the best quality production department. We just want web quality vids with good audio.

So to be expected, I'm having a syncing issue. I'm simply using cheesy 'ole Windows Movie Maker and trying to line up the beginning of the audio from the video with the audio from the audio recorder. That part works fine. But slowly, the audio falls out of sync. You can begin to notice this around the five minute mark, and once the vid gets to 10 minutes, it's almost a 1/2 second or even a full second off.

By reading the link above, I gather the reason for this.

But my question for you video experts, is there anything I can do? I just spent like 4 hours trying to download various freeware programs to try to modify the audio file and make it work...all to no avail. In the process, I did fix one thing that was bothering us...the audio recorder records in mono and we wanted both channels. So I'm using Sourceforges Audacity for this purpose. Fantastic, we know have both channels playing the clean audio...it just isn't synced with the video.

The audio recorder records at 44.1 kHz, whereas the camcorder records audio at 48 kHz. From what I gather reading on your site, that creates a problem right off the bat. And as that link mentions, even if they were both 48 kHz, the reality is that they are two different devices from different manufactures...bound to be some clocking issues.

So bottom line, is there anything easy I can do to fix this. For the life of me, I coulda sworn it worked like clockwork the first few times I synced this up in Windows Movie Maker (years ago). But since then, I've been dealing with this, and it gets REALLY old. So yeah, we need to get donations and save up for better equipment. In the meantime, however, is there anything we can do?

Lastly, on that link, it was mentioned that if you have the exact video clip in "the program" and you have the exact length of the audio clip in "the program", you can then simply "stretch" the audio clip to match the length of the video clip and whala, it works. What program would that be?

Any input would be appreciated.

Thanks in advance.
 
First of all, welcome to DVXUser! You might be surprised to find out that, while many of us here are working professionals, many of the members are also hobbyists and enthusiasts. It's a full spectrum at DVXUser, so don't be afraid to jump right in!

Now, about your sync issue. You have a couple of challenges here. First is recording at 44.1kHz. You camera, assuming that it is set for 16-bit and not 12-bit, records at 48kHz (note: don't use the 12-bit mode if you have it... worthless). Your editing program wants 48kHz for everything to sound its best. Second, any time an external recorder is used next to a camera and the two are not sharing a master clock, the audio is going to see drift.

Audacity should be able to do a bit of what you need, like converting the audio to 48kHz. The other issue is in the drift, and there a couple of ways to handle that.

Drift is not noticeable on short takes. 10 minutes is a really long time for any one clip to be used... is there a reason you are running that long? If you cut the clips up and use them in short clips, you may not see the drift. The other thing you can do is use audacity to compress or stretch the time of the audio, depending on whether the raw audio runs faster or slower than the video. Usually, a very minor adjustment (about 0.01%) in the total time for the audio can do the trick, but you may need to play with it to get the right number. Just keep a copy of the unaltered audio that you can go back to if need be.

If Audacity just won't cut it, you might want to look at something like BIAS Peak for mono/stereo file editing.
 
Thank you for your informative response.

I had given up last night, and then around 2am-ish, I got remotivated when one idea came to mind.

It never crossed my mind to try to bring in the wmv file (from camcorder) into audacity, as that is a video file. But sure enough, it works and simply brings in the audio from the camcorder. Then I can bring in the actual audio (wma) file on a separate track and can eyeball the two tracks. That way, syncing, although still a pain, is doable. You can change the tempo 1 second and see what happens. For me, over a 30 minute period. It changed about .8 seconds.

So horray! It works.

And you are right, if the clips were shorter, I wouldn't have the issue. So yeah, I could make the 30 minute videos into 10 or more clips of 3 minutes each, but then I'd have to somehow do the same for the audio file and then match up all those clips...geez, I feel a headache comming on. That just sounds horrific. But my guess is you probably know something that I don't.

Regardless, it works. Thanks for your help!
 
cazint said:
But my guess is you probably know something that I don't.
Click to expand...

Nope. Truth is, when you deal with non-sync double-system sound, this is what happens. It can be tedious work lining the second-system audio up with the video, but it's a necessary step. The only two options are either to work in short clips or to change the speed of the audio to compensate for the drift.
 
Most people aren't having to do this right?

I mean, most nicer camcorders have microphone inputs, and even most that are over $1000 or so seem to allow for a wireless mic input. It seems as if the need to deal with two streams is removed. Is it often the case that videographers are dealing with this issue, namely, having a video source and a separate, higher-quality audio input source?
 
Hey C2V,

If you were trying to sync 48 to 44.1 and everything else was correct, you would hear the drift after just a few seconds, right?

Thanks
 
cazint said:
Most people aren't having to do this right?

I mean, most nicer camcorders have microphone inputs, and even most that are over $1000 or so seem to allow for a wireless mic input. It seems as if the need to deal with two streams is removed. Is it often the case that videographers are dealing with this issue, namely, having a video source and a separate, higher-quality audio input source?
Click to expand...

The exact opposite. Lots of people deal with this.

On the low end of production (though these cameras are certainly finding their ways into major production now), anyone dealing with a DSLR will likely be dealing with double-system.

On the high end, film doesn't record sound. So sound is a completely separate entity from the camera. Clappers are used for syncing sound to picture in post by matching the frame of video where the sticks meet to the spike in the audio where the sticks clap.

While there are plenty of cameras out there that allow for recording directly to camera with decent results and professional XLR interface, camera audio is and always has been an afterthought for cameras. For newsmagazine-style (ENG) television, recording to camera is most common due to ease of use and low cost and the fact that the camera's recording quality for audio is just fine for 60 Minutes or Dateline NBC. For dramatic/narrative productions, there's probably a separate recorder.

Personally, I record second-system alongside my T2i because there's no other alternative for acceptable results. But I also use second-system alongside my DVX whenever I can, just because I know that I can get better sound even though the DVX has some of the best audio recording of any camera in its class (and even better than some more expensive cameras).
 
Colonel Panic said:
If you were trying to sync 48 to 44.1 and everything else was correct, you would hear the drift after just a few seconds, right?
Click to expand...

Odd question. When are you going to be in a situation where you're playing 48kHz and 44.1kHz simultaneously? The playback system is going to have to convert one of those to match the other, whether it is on the fly or it is rendered out.

Aside from that, the problem is that many consumer/prosumer (and even some professional) devices don't clock to a perfect 48,000 or 44,100 on their own. Some clock just over, and some just under. THIS is where the drift occurs.

If two devices share one master clock generator, then they'll run in perfect sync with no drift... but then, they'd both be recording at the same sample rate.
 
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