I just spent three hours of my life figuring this out, so I thought I'd share it. Perhaps this has been discussed before, but if so, I can't remember it.
The problem is that the Vegas preview window changes video levels, but does so differently on different tracks. However, this only happens in certain preview modes, but does not happen in others.
I have absolutely no idea why this is happening, but I now know how to avoid the problem. I did this in Vegas 10, but I have confirmed the problem (and the solution) in other versions (although not in Vegas 12, because I don't own that).
Here's the "reduced case" that lets me create the problem:
1. I put a a short clip of 60p 1920x1080 video from my Sony CX-700 camera on the timeline in a new project and then rendered to AVI using the "uncompressed" template (the problem shows up when using any codec, but this let me eliminate any codec issues).
2. I put this AVI directly above the original video, on another timeline.
3. I opened the Videoscopes with Studio RGB checked, and the other box unchecked, and "Waveform" display selected.
4. I then muted and then un-muted the top track while watching the scopes.
When I did this, the entire levels shifted up by about 3-4 when I viewed the uncompressed copy of the original. This shift should not happen.
What I describe above is my final, "reduced" test case. The original workflow was far more complicated, but involved frameserving and denoising. I couldn't understand in that workflow why I was getting this level shift, and it makes even less sense in this simple, reduced case.
There was nothing different about the tracks, and I even duplicated the original track, deleted the original video and then placed the uncompressed version on that track. The levels shift persisted.
I was doing this in Vegas 10, but when I tried it in Vegas 8, I had no problem.
Hmmm .....
Well, to make a long story short, I finally figured out why Vegas 8 gave me no level shift (which is what should happen) and Vegas 10 did shift the levels:
It was my preview settings.
When Vegas (any version that I've tried) is set to "Preview Auto" you will get the levels shift on uncompressed video. This also happens with video that has been rendered using DV AVI codec (which also involves down resn'g to 720x480), Cineform, HuffYUV, etc.
If you change the setting to Preview Full, the problem goes away.
I tested all the other preview settings, and until you get to the series of Best preview settings, at least one of the settings in the other three preview modes has this same problem.
I have no idea why this happens, but I think this probably explains why so many people were reporting different results in many of those long, tortured threads that explored why we were seeing level shifts when comparing uploaded material to the original. Don't misunderstand what I'm saying: in those threads there were most definitely other reasons why there were levels shifts. However, part of trying to figure out those shifts sometimes involved putting results back on the timeline and then muting and un-muting tracks while looking at the Vegas waveform scope. In those cases, this preview setting anomaly will definitely cause a problem.
For those who are interested (Sony??), here is my test case, created in Vegas 10:
Levels Test Case
It contains the veg file, the original mts 1920x1080 file from my camera (a short clip resulting from accidentally pressing the record button), and an AVC file rendered from Vegas. Don't worry about the codec used (AVC) because it doesn't make any difference to the test. Open the veg file and set the preview setting to preview-auto. Watch the Waveform monitor in the scopes. As you switch between the two files, you will see the levels shift up and down. This is easiest to see on the bottom right of the levels display. Switch to Best-Full, repeat the test, and notice that there is no shift in levels (although there is a slight spread because of changes made by the codec).
I hope this helps someone. Perhaps someone from Sony can explain why this is going on.
P.S. Here's the original:
and here's what the scope looks like with the level shift:
The problem is that the Vegas preview window changes video levels, but does so differently on different tracks. However, this only happens in certain preview modes, but does not happen in others.
I have absolutely no idea why this is happening, but I now know how to avoid the problem. I did this in Vegas 10, but I have confirmed the problem (and the solution) in other versions (although not in Vegas 12, because I don't own that).
Here's the "reduced case" that lets me create the problem:
1. I put a a short clip of 60p 1920x1080 video from my Sony CX-700 camera on the timeline in a new project and then rendered to AVI using the "uncompressed" template (the problem shows up when using any codec, but this let me eliminate any codec issues).
2. I put this AVI directly above the original video, on another timeline.
3. I opened the Videoscopes with Studio RGB checked, and the other box unchecked, and "Waveform" display selected.
4. I then muted and then un-muted the top track while watching the scopes.
When I did this, the entire levels shifted up by about 3-4 when I viewed the uncompressed copy of the original. This shift should not happen.
What I describe above is my final, "reduced" test case. The original workflow was far more complicated, but involved frameserving and denoising. I couldn't understand in that workflow why I was getting this level shift, and it makes even less sense in this simple, reduced case.
There was nothing different about the tracks, and I even duplicated the original track, deleted the original video and then placed the uncompressed version on that track. The levels shift persisted.
I was doing this in Vegas 10, but when I tried it in Vegas 8, I had no problem.
Hmmm .....
Well, to make a long story short, I finally figured out why Vegas 8 gave me no level shift (which is what should happen) and Vegas 10 did shift the levels:
It was my preview settings.
When Vegas (any version that I've tried) is set to "Preview Auto" you will get the levels shift on uncompressed video. This also happens with video that has been rendered using DV AVI codec (which also involves down resn'g to 720x480), Cineform, HuffYUV, etc.
If you change the setting to Preview Full, the problem goes away.
I tested all the other preview settings, and until you get to the series of Best preview settings, at least one of the settings in the other three preview modes has this same problem.
I have no idea why this happens, but I think this probably explains why so many people were reporting different results in many of those long, tortured threads that explored why we were seeing level shifts when comparing uploaded material to the original. Don't misunderstand what I'm saying: in those threads there were most definitely other reasons why there were levels shifts. However, part of trying to figure out those shifts sometimes involved putting results back on the timeline and then muting and un-muting tracks while looking at the Vegas waveform scope. In those cases, this preview setting anomaly will definitely cause a problem.
For those who are interested (Sony??), here is my test case, created in Vegas 10:
Levels Test Case
It contains the veg file, the original mts 1920x1080 file from my camera (a short clip resulting from accidentally pressing the record button), and an AVC file rendered from Vegas. Don't worry about the codec used (AVC) because it doesn't make any difference to the test. Open the veg file and set the preview setting to preview-auto. Watch the Waveform monitor in the scopes. As you switch between the two files, you will see the levels shift up and down. This is easiest to see on the bottom right of the levels display. Switch to Best-Full, repeat the test, and notice that there is no shift in levels (although there is a slight spread because of changes made by the codec).
I hope this helps someone. Perhaps someone from Sony can explain why this is going on.
P.S. Here's the original:
and here's what the scope looks like with the level shift: