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I make a 30 second recording using a webcam on a laptop. When I play the .avi file afterwards, the audio and video are out of step. The sound starts arriving about a second after it should do and gets increasingly delayed.

Why is this?

Whilst I am making the recording, I can see the video that is being captured being displayed on the laptop monitor. I can actually get lip synch if I s-p-e-a-k l-i-k-e t-h-i-s.

I clap my hands at the start of the video. When I watch the video afterwards, the sounId is delayed by about a second.

The audio track continues for about ten or so seconds after the video component has finished. (A still image remains in the video player while the voice continues.)

I can fix this problem after the recording (laboriously), but I want to have the recording work properly in the first place.

The webcam is a BisonCam NB Pro integrated into the laptop. It is a 2 Megapixel camera that can record at 15 fps. The CPU is an Intel dual core T4200. The machine has 4GB of RAM. I am saving the recording to a file on a ramdisk, so I don't think the hard drive is the problem. I am using BisonCap to record, the software that came with the computer. I have set recording for 15 fps.

Please help!

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You should check your recorded video with MediaInfo. Regarding your problem, it shows,

  • if the durations of the video and the audio is the same or not,
  • if the interleave of the audio (the starting offset) is set correctly
  • in which sampling rate your audio was recorded.

Then, I would import your video file into Audacity (which imports only the audio, of course).

  • On the left side of each track you find the sampling rate, too. Is this the same sampling rate as being reported by MediaInfo?
  • Does Audacity play the audio too slow, too?

My impression from the symptoms that you describe is that the audio is recorded at a certain sampling rate, but reported as a lower sampling rate, or not at all.

Try to modify your sampling rate, either in your recordings settings, or in the Windows system. On Win7, it's under Control Panel->Hardware & Sound->Manage Audio Devices->Recording. There, select your microphone, then Properties->Advanced. There you can change the sampling rate.

If changing the sampling rate doesn't help, then you can only try another webcam software, or record the audio independently.

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There are quality settings for both the audio and video recording. Have you checked out the video capture settings? Maybe some adjustment here would get the audio and video back in sync.

Video Stream Format Properties

The picture is from this Dell support site. May be some more useful info there.

Also, just in general (sorry if it's obvious) are you sure your drivers for the webcam are up to date?

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Best way to check if it's out of sync or drifting, or both would be make a recording, clap with your hands once at the beginning and at the end. Check if the sound is earlier or later at the beginning or the end. Then to resync, use an Non Linear Editing program to align and possibly re-time the audio, retiming the video will look much worse than fixing the sound. Also recording at 15fps rather than 30 won't look great.

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I think you should try another program first and see the result. Maybe the software is the reason or tweak the settings of yours. Also try to close any other software which is running at that time like antivirus programs etc.

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