Audio/Video Sync/Adjustment Limitation?

[hsinhow]

This seems to be a hot topic recently...

I began to work on multi-camera video project where I need to synchronize two video/audio streams together. Since VS does not provide automatic audio synch function, I have to manually align audios from different sources. What I found is that there seems to be a minimum time step size you can move a clip. Thus, I can say that I never be able to perfectly synchronize two sources. However, the minimum time step size is probably small enough so that we don't obvious delay in most cases.

This been said, for certain scenes, such as filming a piano recital with closeup on the player's hands and keyboard, this difference can become detectible.

Any comments? What about other video editors? Do they have similar limitations?

HH

[BrianCee]

Yes the minimum time you can move a clip is one frame - you can't split a video much smaller than that

You may find alignment easier if you put a short plain colour block at the left hand end of each video track you use - say black of around 1 second duration and make sure the video clips are butted to it.

you can now change the duration of the block in the top video track up or down at one frame at a time - since the clips in the top track always butt to the left the videoclip will then move a controlled one frame forward or back at each adjustment.

[hsinhow]

Interesting and useful technique. Thanks.

From what you mentioned, the duration of a color block is also bounded by frame size, right? Who determined the frame size? Is it the project property, i.e. 30 fps, 60 fps? By selecting 60 fps setting, can I make the frame size smaller regardless of the video source's fps?

It seems that VS's max fps is ~60.

What about audio only tracks? Sine audio does not have frame size (am I right?), can I move audio in finer step sizes?

HH

[BrianCee]

You determined the frame RATE - not size - when you first filmed the video - you chose 25, 30. 50 frames per second - whatever ?

if you do not stick with the same frame rate then your video will not play at the correct speed.

If your video is 30fps then each frame is 1/30th of a second - that is 0.033 seconds - no one is going to see audio lag/lead of that duration.

[hsinhow]

You are correct. Frame rate is the right terminology.

My thought is that if we create a 60 fps project, the color block's minimal time step should be 1/60th second. Then the video/audio clips (assume that they were taken at 30 fps) should be able to be aligned to 1/60th second.

Can we do this? I am always puzzled about the relationship between the project setting and final rendering format in VS. For example, I use HD (1920x1080) project setting all the time but I can choose whatever output format in the Share section.

HH

[lata]

Hi

Where possible you should set your project properties to match your video files properties, this will set the timeline to either 60 or 30 fps and also match the resolution 1920 x 1080.

For a 60 fps video you will see all 60 frames on the timeline, if you add a 30 fps to this project additional / duplicate frames will be added effectively making the 30 display as 60fps.

The other way around, using 30 fps project properties, add a 60 fps video and frames will be removed, every alternate frame will be removed to allow the 60 video to display on a 30 platform.

Clear as mud.

Note:-
Make sure you have Settings – Preferences – Show Messages………. ticked
Start a new project and add your video, in most cases you will be asked to match the project properties.
Always check your project properties when working with different frame rates.

I would set my frame rate to match my output format, so if I intend to burn a Bluray disc then 30 fps.