VS 2018 Constant verses Variable Frame Rate Render

[Dukepac76]

I have noticed that after rendering a Fraps captured AVI file to an MP4 video, some of my MP4s are converted with a constant frame rate and some are variable frame rates. Can someone please explain to me how the program determines which way to go when rendering a video file? Is there a way that i can control whether it will be constant or variable? Thank you.

[Ken Berry]

Welcome to the forum.

I had been under the impression that Video Studio could not deal at all with variable frame rates, let alone produce them. It often refuses even to allow a clip with a variable frame rate to be inserted in the timeline, and we usually advise people with that problem to first convert to a constant frame rate. And by constant frame rate, I am referring to the variety of choices of fixed frame rates such as PAL's 25 or 50 fps; NTSC's 30 or 60 (more correctly 29.97 and 59.94 fps).

So it would be useful if you could tell us what range of variable frame rates you are seeing coming out of VS...

Constant vs. variable bitrates are, of course, a different matter entirely...

[Dukepac76]

Thank you Ken. I am currently exclusively filming at 60fps (59.94) and this is what I am rendering in VS. The results are "variable" with some coming out as a fixed frame rate and some as variable.
So here are some I just finished with a short time ago. All were filmed at 60FPS and the rendering was done with the following settings:
MPEG-4 Files
24 bits, 1920 x 1080, 59.94 fps
Frame-based
H.264 High Profile Video: 20000 Kbps, 16:9
48000 Hz, 16 Bit, Stereo
MPEG AAC Audio: 192 Kbps

Here are two results one with constant frame rate and the other variable and I have no idea why except that it is my desire that they all be constant.

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 2 Ref Frames
Format settings, CABAC : Yes
Format settings, RefFrames : 2 frames
Format settings, GOP : M=3, N=30
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 5 min 18 s
Bit rate mode : Variable
Bit rate : 18.0 Mb/s
Maximum bit rate : 20.0 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 59.940 (59940/1000) FPS
Minimum frame rate : 59.880 FPS
Maximum frame rate : 59.940 FPS
Original frame rate : 59.940 (60000/1001) FPS
Standard : NTSC
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.145
Stream size : 683 MiB (99%)
Language : English
Encoded date : UTC 2018-03-12 19:18:01
Tagged date : UTC 2018-03-12 19:18:01
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 2 Ref Frames
Format settings, CABAC : Yes
Format settings, RefFrames : 2 frames
Format settings, GOP : M=3, N=30
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 4 min 26 s
Bit rate mode : Variable
Bit rate : 18.3 Mb/s
Maximum bit rate : 20.0 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 59.940 (60000/1001) FPS
Standard : NTSC
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.147
Stream size : 583 MiB (99%)
Language : English
Encoded date : UTC 2018-03-12 18:40:29
Tagged date : UTC 2018-03-12 18:40:29
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

So I trying to figure out the controls for being in variable verses constant. It seems to be an automatic application by the software but I have no clue how it determines what mode to render in. Thanks