--- On Mon, 8/29/11, Lee Menningen <[email protected]> wrote:
> Question: Wouldn't this be a problem
> with ANY audio recorder? After all, the
> rate at which audio is recorder and the rate at which video
> is recorded is
> determined by the internal clocks of the recording device.
> It would be
> almost impossible for two such devices to have exactly the
> same clock rate,
> so aren't we actually talking about "close enough" rates?
> Meaning that with
> 5-minute clips one might not notice the difference in
> speeds, but recording
> an 80-minute event might experience significant drift?
That's why time code was created for analog recordings. With digital video and
audio, it *should* be much simpler to keep them synchronized because the frame
rate is exact and the audio is so many samples per second.
But the way things have developed, there are several ways for digital audio and
video to get out of synch. Sometimes the whole thing is just offset a bit so
correction is a simple matter of shifting the audio to video alignment then
padding one or the other with silence or blank video or a still image.
Another way they can get wrong is if the video frame rate is changed for some
reason, say from 24 to 23.976, without a corresponding speed change in the
audio, processed to keep the pitch the same.
Digital audio connections between pieces of equipment do have timing data. Do
some Googling on S/PDIF and TOSLINK (which is 'simply' an optical version of
S/PDIF).
It does strike me as odd that with an all digital workflow from end to end that
it's ever possible to get out of synch audio and video. It has to be either an
error in software or firmware, or software and/or firmware written with options
that allow humans to make improper option choices that result in
synchronization problems.
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