Audio and Video Synchronization Problems

dpaterso wrote on 2/9/2003, 1:58 AM

Hi,

I know that this is not a Sonicfoundry / Vegas problem but it does seem that this is a common issue (after searching the net) so (maybe) any replies to this message will help others with the same problem.

I have been experiencing the same problem for over a year now and I do not seem to be able to solve the problem no matter what I have tried so this message is posted in desperation.

The problem is as follows:

When capturing video and audio (regardless of the capture application being used) everything seems to be OK as long as the capture duration is short i.e. a couple of minutes or so.

During a lengthy capture the audio and video synchronisation becomes progressively worse i.e. in the beginning everything is fine but toward the end of the capture the video is about a second ahead of the audio in a capture of about an hour or so.

The strange thing is that no matter what capture application is used no dropped frames are reported.

Making the master stream the video, audio, or none, does not seem to change anything (other than the length of the streams BUT in a short capture it is usually only the audio stream that is slightly longer when enlarged but it would appear that this is only because the capture of the video stops a split second before the audio capture i.e. in a short clip the audio and video is still in synch).

Various codecs / compressors e.g. PIC Video MJPEG have been tried and still no change. The problem also occurs with no compression.

Could this be a driver problem?

Are there any discussion boards dedicated to this issue?

Does anyone know of any documentation or white papers that address this issue?

Could this be a hard disk drive problem (see below) i.e. would it help to use a drive such as Western Digitals 120GB 7200RPM with 8MB cache?

For reference puposes I am using the following hardware / software:

AMD Athlon XP 1700+ (runs as 1.4GHZ)
512MB DDR RAM
2 X 20GB 7200RPM IDE HDD
32MB GeForce MX AGP VGA
Lifeview TV Tuner / Video Capture (by Animation Technologies)
HI8 Camcorder (analog)
Windows 2000 Professional SP3
DirectX 9
NTFS
Drives are formatted prior to each capture (as opposed to defragmentation)

Capture is normally at 352 x 288 and 32bit color with audio at 44100khz stereo (PAL VCD Standard).

Regards,

Dale Paterson
dpaterso@fleetfocus.net

Comments

pwppch wrote on 2/9/2003, 5:17 PM

Sample rate clock is not accurate is my first guess.

If your analog capture card does not have a clock rate that is locked to a common clock, then there will be drift.

44.1 kHz on one audio card is not the same as on another card. Also, if the video playback device is not sycn'd to a common clock, then timing will be off.

It is not cheap to solve this problem. You will need to set up a common clock system that will be the slave to your video sources and your audio inputs/outputs.

However, in Vegas you can easily adjust the audio portion of your capture to line up exactly with your video. You can then render this out to a new file and you should have a sync'd audio and video source to work with.

Peter

dpaterso wrote on 2/10/2003, 12:07 AM

Peter,

Thanks for the reply - I think I know what you mean!

It would be easy to synch the streams manually if they were out of synch from start to finish by the same amount but this is not the case - during a lengthy capture of about 2 hours - the beginning is fine - about 10 or 15 minutes later it might be out slightly - and by the end it is about by a substantial amount.

Does this same phenomenon occur with digital video and firewire capture?

Dale.

SonyEPM wrote on 2/10/2003, 10:27 AM

"Does this same phenomenon occur with digital video and firewire capture?"

No- if you capture DV you'll never have this problem.

nlamartina wrote on 2/10/2003, 9:42 PM

Dale,

The problem is probably with your capture device. It's likely using NTSC Non-drop format to capture, meaning it's capturing literally 29.97 video frames per second and 30 audio frames per second. Over time, this will cause drift that gets worse with time. Here are some tips you can use to keep the synch together when rendering:

1. Set your project default timecode to "SMPTE drop" in "project properties".
2. Avoid rendering your final copy at a lower framerate than the material present in your project, ie, using material that is 25 fps and rendering at 15 fps. Try to be
consistant as possible.
3. If the recorded/captured material in out of synch, first place it in your project. Hold down your control key. Left click on the end of the audio stream and drag it inward until the audio lines up properly (preview to check). Generally, use 1.2 second for every 20 minutes.
4. Click here for information on SMPTE timecoding. It will clear things up a bit for you.

If need any more help on the subject, write back here. I'll be glad to help.

- Nick

bbbakke wrote on 2/24/2003, 4:25 PM

Does anyone have a good avi for testing av sync? What I am looking for is something like you would see at the beginning of a movie years ago. A beep 1 a second with a spinning clock like image and a numerical count in the center?

musicvid10 wrote on 2/25/2003, 12:51 AM

I use a clip of a basketball practice to check sync. The dribbling is a dead giveaway if the sync is off even a tiny bit.

There's an old countdown clip with a beep at www.archive.org