Vegas is rendering frames it shouldn't

[tripecac]

I'm using Sony Vegas Movie Studio 8.0c.

Vegas seems to be rendering frames that I cropped out. This occurs when I split clips and then crop a few frames from the beginning of the second clip. When Vegas renders, it's including some of the cropped frames.

For example, there's a shot where someone enters a store, and then in the next shot, a dog runs toward the camera. I split the clip between those two shots, and deleted a few frames from the beginning of the dog shot.

When I play back the video frame-by-frame in the Vegas preview window, the dog starts with his foot and tail in a certain position. When I render to mpg and view the mp3 in VirtualDubMod (or on a DVD), the dog shot has 3 or 4 extra frames before the first dog frame in the preview.

Also, if I zoom in on the time line in Vegas, I see that first dog frame is consistent with the preview window. So it's not the preview window that's "broken"; it's the rendering.

So, Vegas seems to be un-cropping a few frames when it renders. How can I prevent this from happening? I want the rendering to exactly match the frames in the preview.

Thanks!

[tripecac]

Here are screen grabs to illustrate what I'm seeing:


20080716-extra-frames.gif

[jagabo]

I don't use Vegas but here's a thought...

Are you editing the video after it's been converted to MPEG2? And using a non re-encoding editing process? That would explain the extra frames at the start of a clip. Each clip has to start on a keyframe. Vegas automatically started your clip at the keyframe prior to the start frame you selected. MPEG files will typically have keyframes every 12 to 15 frames.

[tripecac]

Are you editing the video after it's been converted to MPEG2

No, I'm not editing the mpg after I render it.

Are you saying that the mpg will always contain extra frames? Yikes! How can I prevent Vegas from rendering those extra frames, the ones I'm intentionally removing (because of the static you see in that first rendered dog frame)?

[tripecac]

I just tried a test where I rendered about 1 second of video, right before and after the cut with the dog, using different rendering options. For everything I tried (avi, mpg, burn-it-to-dvd wizard), the rendering worked correctly; no extra frames were added.

However, I'm remembering something now... As soon as I noticed the burst of static on the DVD (see the first rendered dog frame), I loaded my project in Vegas in order to remove that bad frame. I never found it. I did, however, remove another frame or two, due to weird coloring. So I no longer think 3 or 4 frames were added. Instead, I think just one frame was added.

This gets me closer to understanding what might be happening.

If Vegas previewing is progressive, but output is interlaced, then maybe the static frame was an "odd half-frame", and therefore not displayed.

So the question is: how can I get Vegas to show me interlaced previews, so that I can see exactly the same frames that will be rendered?

[tripecac]

Oh wow, I just confirmed the above idea...

When I monitor Vegas with my standard DV, I can see the frame with the static. On the computer, I don't see any static. So I guess I can do all my editing while monitoring on the standard TV, although that is tedious. I wish I could get Vegas to show the interlaced video during preview.

[jagabo]

Use VirtualDub to view your DV. It shows you what's in each frame of the video, no deinterlacing.

Are you saying that the mpg will always contain extra frames? Yikes!

No, I'm saying if you edit MPEG footage with an editor that only cuts on keyframes you can not get frame accurate editing.

[tripecac]

Use VirtualDub to view your DV. It shows you what's in each frame of the video, no deinterlacing.

So if I want to be able to remove bad (interlaced) frames, I need to use VirtualDub instead of Vegas? That means I'd be editing the DV-AVI rather than the mpg, correct?

if you edit MPEG footage with an editor that only cuts on keyframes

I think Vegas is cutting correctly. However, the previewing on my computer monitor is progressive. The same frame on the TV is interlaced (I can see both at once). So, Vegas knows the static-filled frame is there... It just isn't showing it on the computer monitor, because the preview is progressive.

At this point I think my question boils down to this (which is very Vegas-centric):

How can I get Vegas to show interlaced previews on my computer monitor (so that I don't have to keep monitoring on the standard TV)?

[SLK001]

Your problem is Vegas doesn't seem to be able to do what you need it to do.

As has been suggested before (many times) VirtualDub will probably give you better results.

Even better, you should learn how to use AviSynth. With it, you should be able to "breeze" through your editing.

[tripecac]

Okay, I figured it out!

In the Preview window, I needed to change the quality to one of the following:

1) Preview (Full)
2) Good (Full)
3) Best (Full)

Now the preview window is interlaced, and I can see the bad frame.

Problem solved!