A 23.98FPS video rendered in 29.97 retains the same runtime, why?

[skribby]

I had a 23.98FPS video, added into Vegas, where the project settings was 23.976FPS.
Then, I rendered the project in 29.97FPS.

I figured if I would render a video in a higher framerate, the renderer would have to squeeze in extra frames to account for the higher framerate, and thus increasing the runtime of the video. I reviewed the rendered file; it is detected by PotPlayer as 29.97FPS.

Yet, my video is the same length. How is this possible? am I just really dumb and missing something here?

[SameSelf]

Well, I am not a Vegas user. But it sounds like Vegas telecined your footage i.e. it used 3:2 pull down and duplicated frames to maintain the same time. If you want to speed up your footage instead, I would think that Vegs has some retime controls versus changing the timeline framerate.

[jagabo]

Vegas isn't simply playing the same number of frames at the higher frame rate. It duplicates frames (or fields, with or without blending) to create 5 frames from every 4 source frames. Since there are now 25 percent more frames a 25 percent faster frame rate results in the same running time.

[skribby]

Oh I get it.

Vegas creates extra frames to maintain the runtime. i.e if it hadn't created the extra frames, the higher framerate would result in a shorter than original runtime, right?

This means my initial question was a bit backwards

[SameSelf]

Theoretically, yes. If you take a film strip meant to be played back at 24 fps and run it at 30 fps, it will be sped up by 1.25x. However, if Vegas hadn't duplicated frames, then that likely becomes a timecode issue and would most likely result in stuttering playback. Others may correct me on this though.

What exactly are you trying to accomplish? Are you trying to telecine your footage or actually speed it up?

[skribby]

No, not trying to do anything.

I just noticed that I had accidentally rendered in 29 instead of ~24, and noticed that the runtime was the same so I had to find out why it works that way.

thanks for the info guys

[johnmeyer]

As a long-time Vegas user, I can tell you exactly what it does.

Vegas is designed to let you mix video from different cameras on the same timeline. This includes mixing footage shot at different frame rates. The only way this can work is if it "conforms" all footage to the same frame rate. The rate chosen is the one you set in project properties although (and this is important) if you choose to render at a frame rate that is different than what you choose for your project settings, it will then do the same "conforming" but this time will match what you set in the "Render As" template. Put another way, the frame rate chosen in the Project Properties is only used during timeline playback and does not affect the render.

Others have already told you how Vegas changes video frame rate: it either adds additional frames and/or fields (e.g., to take 24p to to 60i) or it deletes fields or frames if you ask it to go the other way.

One final thing you should know is that when Vegas adds fields or frames, it can do so in one of two ways, depending on how the "re-sampling" setting is set. This can be set differently for every single event on each timeline. The default (until the new Vegas 14) is "smart resample." When set to this (or if set to "force resample") Vegas adds fields or frames when needed, and the new frames created are produced by blending the proper amounts of adjacent frames. The blends are exactly the same as what you get from a cross-fade, i.e., you get a frame that actually shows both adjacent frames simultaneously (i.e., you can see a ghost of both images). If you instead set the event to "disable resample" the additional frames are created by duplicating either the preceding or succeeding frame, whichever is closer in time. This creates a sharper result, but with jerkier motion.

[skribby]

Thanks!