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| How to fix gradual loss of sync once and for all |
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| User
comments | Printer-friendly
version of this page | Guide
made by Acidagent | |
How to fix gradual loss of sync once and for all
Ok i guess this topic has been covered quite a few times. So i'll try and make it quick.
Now Phat J's guide did give me some clues, but he overlooked a simpler, more accurate and quicker solution. I guarantee and promise this will work. Basically you need to resample rather than compress or expand the time. The example I've done here works for MPEGs but you could apply the same methods for AVI files.
Unbeknownst to most people I should imagine. Sound cards suggest they are record at 44.1KHz. Well in most cases they probably do. However, sometimes they don't quite sample correctly and are off by about 0.005KHz. This is what causes your gradual sync people. Some guitarists may recognise this if you have a software tuner. You need to calibarate the soundcard to get the perfect tuning.
The method will also work with VHS captures too, even if you capture other sources and they are in sync.
Is everybody in, is everybody in, so let me begin.
You will need:
Sonic Foundry's Sound Forge or Cool Edit (Both are available as demos)
TMPGenc
VirtualDub
1. Similiar to Phat J's guide
Use VirtualDub to find a time in the video to find a noticeable sound. It helps if you can lip-read but it's not essential. Make a note whether the sound is behind or before the video.
Here I've found a frame from the Let It Be film, where John is going to sing the word "Seeeeee" from the song I've Got A Feeling.
Jot the time down, in this case it's 1:16:22.891. The audio is ahead.
2. Use TMPGenc and under MPEG Tools to demultiplex the MPEG file into two separate files. So in this case it would Let It Be.m1v for the video and Let It Be.mp2
3. Open your audio file in Sound Forge (This may take a while if it's huge) and find your jotted time. Play the sound and note the where it's playing.
Here you can see the beginning of the "Seeee" peak and the audio is about 0.939 seconds ahead out of sync.
4. Now here's the amazing part. Instead of expanding or compressing the sound, we're going to adjust sample rate of the sound instead. Under Process you will find an option called Resample.
Make sure you only set the sample rate first only. Here i've added 9Hz because the sound was ahead so it needs to be played ever slightly more quickly. Reduce the sample rate if it's behind. You'll have to tinker with the sampling rate, but you'll find that adding 1 Hz will reduce about 0.1 seconds off over an hour. Don't worry about the pitch change, it's doesn't make a difference due to such a small change.
Now you can see i'm only 0.002 seconds out. This is alot more accurate than the time expand/compression utility. Not only that, you don't have to render the effect to preview, so you don't have to wait ages if you've got a big file. Some soundcards won't play at 41,109Hz but this really isn't a worry.
5. Once you've found the correct sample rate, you need to resample. So this time go back to Process and Resample and clear the box that says: "Set the sample rate only(Do Not Resample") and adjust the new sample rate to 44,100Hz. You don't need to apply an anti-aliasing filter, the resampling difference is so small to justify the time taken to apply the filter. Once you've set it it will start to resample which may take a while.
Now you can see your sound is at 44,100Hz and the sync is damn as near correct as it can be. No amount of time expanding/compression can get this close.
6. Now all you need to do is save the file. You'll have to save it as a Wave File at 44,100Hz Stereo unfortunately, which means mega space, but it'll be worth it.
7. After you've saved it, use TMPGenc to change the wav file into an mp2 file.
8. Use TMPGenc again and goto MPEG Tools and select Multiplex. Here it would be Let It Be.m1v as the video and Let It Be.mp2 as the audio. Choose anything you want as the output file( well make sure you end it .mpg or mpeg)
9. Enjoy your newly synched video.
10. Praise me for wasting hours trying to sort this out once and for all. I really do believe you can't get any more accurate than this method and it works with humungous files.
So to cap off, blame the soundcard, it's not recording at the correct sampling rate it's supposed to. The soundcard in this case actually records at probably about 44,109 to 44,110Hz. Perhaps video capturering software needs to use an audio calibrating utility like guitar tuning software does to help with the sampling rate and synch.
Thanks to Phat J for spurring me a bout of inspiration and thanks all for those in sync-hell. Welcome to uniformity.
Yours in humanity
ACID Agent
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