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Old October 19th, 2011, 11:05 PM   #16
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Re: Compact digital recorder that doesn't lose sync?

-- Not sure what you mean by "pull up" the video

I mean slide the video clip in the timeline so that it syncs with the audio.

-- I'm curious as to why you would rather play with your video playback rate rather than the audio.

Because most tools I have used leave artifacts in the audio when you diddle with the the timing. Anomalies ranging from mild to horrid. This is not only my experience but that of others who have discussed this before in this and other forums. OTOH, moving the video to match the audio is undetectable by most viewers.

-- Whenever you adjust the frame rate of the video you can experience many more problems with artifacts.

Agreed. Which is why I don't adjust the frame rate. And you make my point about artifacts from trying to adjust timing/pitch in general. Simply sliding the video into sync does not involve changing its length or frame rate.

-- You also are forcing the video to rerender every frame. So if you do happen to shoot and capture in a codec that is for final delivery you are needlessly adding to the processing time.

Which is another reason I don't do that. (And again doing it to the audio track forces a similar re-rendering.)

-- I have seen some really strange artifacts pop up in the video when trying to adjust by only a few frames over an hour.

Again, which is why I don't recommend diddling either the video or the audio. You will hear strange artifacts in the audio throughout if you try to stretch or shrink the track.

-- Video should only be adjusted by whole frames

IME, neither video nor audio should ever be "adjusted". The process does damage to both audio or video, but it is much more noticeable in audio than in video.

Any video with a single shot long enough to go out of sync will be deadly dull. Any point where an audio or video edit is made is a perfect opportunity to "pull-up" (or "re-sync") audio and video. This is actually much easier than it sounds. It is also inherently immune from shrink/stretch artifacts in either audio or video.

IME, also audiences are much more forgiving of adding or deleting a single frame of video to pull up the sync than having to put up with audio artifacts throughout the production.

-- You can however adjust the audio by any length without the same nasty effects.

That is most definitely NOT my experience. I would avoid doing that at any cost. Fortunately there are very easy ways of avoiding that.
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Old October 20th, 2011, 12:35 AM   #17
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Re: Compact digital recorder that doesn't lose sync?

Adjusting the speed of audio can be done without causing gross artifacts, though people with golden ears will certainly disagree. Stretching audio will, however, cause gross artifacts when you try to change the time and preserve the pitch or when you try to change the pitch and preserve the time.

I would approach it differently, depending on the project.
1) A narrative piece with lots of cuts: Just sync the start of each segment. No processing needed for short clips.
2) A long, continuous speech: I'd stretch the audio as needed. Or, if you have time, cut it up during pauses every few minutes, sync each segment, and blend the background sounds to eliminate gaps.
3) Music video: Don't touch the audio. If you have cuts, it's no problem. If it's a continuous live shot, you can probably add/drop frames when there is little motion without problems. If that's not working (say for a moving steadicam shot), stretch the audio.

The best approach really depends on the situation and the amount of time you have available.
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Old October 20th, 2011, 01:43 AM   #18
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Re: Compact digital recorder that doesn't lose sync?

Richard,

In general I would have to disagree with your assessments for the specific types of productions I'm thinking of, single camera continuous running shows that have both dialog and music. I would agree that the best way would be to cut either the audio track or video track and drop the necessary length. I would have to say that I have not experienced the audio anomalies that you've experienced. As Jon noted, if you try to maintain pitch while applying a time stretch you can experience them but I don't think anyone can hear the difference in pitch of stretching three or four frames over an hours time. I would however believe that most people would see a dropped frame or added frame once every 20 or 15 minutes unless you had a cut or black frames to hide them in.

As Jon said, the best solution really depends on the situation. The universally best solution of course is to genlock the audio and video but of course that's a very costly solution.

-Garrett
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Old October 20th, 2011, 02:48 AM   #19
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Re: Compact digital recorder that doesn't lose sync?

Quote:
Originally Posted by Jon Fairhurst View Post
Adjusting the speed of audio can be done without causing gross artifacts, though people with golden ears will certainly disagree.
Perhaps that is the perspective here. While I certainly don't consider myself "golden ears", I was compelled into getting into video because of the generally deplorable state of audio for video. I've been seriously into video for only around 20 years, but more than twice as long as that in audio. And more than half of my video production (and all of my audio) projects are completely or partially music performances. But even for single-camera "talking head" stuff, I shoot at least a few minutes of audience reaction and other "B-roll" type footage to cover whatever I need to do with the primary footage.
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Old October 20th, 2011, 05:09 AM   #20
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Re: Compact digital recorder that doesn't lose sync?

Quote:
Originally Posted by Jon Fairhurst View Post
..
The best approach really depends on the situation and the amount of time you have available.
The BEST approach is to avoid the issue all together by using cameras and audio recorders that either a: have good enough clocks to maintain sync over the duration of a typical shot; or b: use cameras and recorders that send and accept external sync so you can use one of the strategies to provide a common timebase to keep everything in order regardless of the shot length.
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Old October 21st, 2011, 10:48 AM   #21
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Re: Compact digital recorder that doesn't lose sync?

Very interesting discussion. Now I'm wondering if it would be better to either clip out or duplicate a couple of frames worth of Audio where there are undefined sounds such as applause then do a short cross fade to mask the cuts so that is is not audibly detectable.

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