Need help understanding framerate


(Skyfish) #1

Hello, I need some help with video editing and framerate. I hope I posted this in the right place.


The frame rate is set to 10. I could swear I set it to 30 when I started my project and when I double checked it. 1: How did it become 10? My oldest back up save also has a frame rate of 10 so I assume it happened early on. If I change the framerate, all the timings of my cuts and audio become messed up. (the cuts happen at the wrong moment in the clip) I would like to understand how this happened and how to avoid it in the future. 2: Did I hit a button accidentally, or did I select a preset that chaned my settings and not notice? My source file is 30 FPS. 3: Will I have to redo the entire project (re cut the footage and re align the audio in order to get a frame rate of 10?)

I would also like to understand better the difference between a soft and a hard cut, I have used mostly soft cuts. occationally I found that my cuts didn’t “take effect” and I would have to use a hard cut, 4: does anyone know why that is, maybe a common noob mistake? 5: What is best practice in a project like this? (boring tutorial video on how to navigate a boring website, audio is important)

Some background to understand my nooblevel: This is my first time editing video in blender, and my 3rd time editing any video at all. (the first two were my final major illustration projects in after effects, where I also had to redo the entire thing because of wrong frame rate (puppet warp keyframes) and you’d think me being cautious this time would avoid this but noooo) the second was in premiere pro and I had no issues.

6: I would like to understand the relationship between framerate and editing cuts a bit more. Why do all the timings get messed up when the framerate is changed, when the source videos all have 30FPS? I would have assumed that blender stores my “cuts” as a time stamp associated with the video clip, so the change of frame rate shouldn’t really matter, clearly I am wrong about something… please enlighten me…

7: when I render my video out, it appears to be playing extremely fast, maybe there is too few frames? It also includes frames that I initially cut out. It does not look like my preview at all. What is going wrong, here? I did a test render of 4 seconds of video, but only 1 second has all the frames in it.

Thanks for any help you can give.


(Gaeriel) #2

Blender adjusts the frame rate automatically to the frame rate of the first video you import. You can see that is the correct frame rate for the first few strips because the audio strip lengths match. Also, it’s set to 1000 fps, not 10 fps. You probably imported a video made with Blender 2.79 which had a bug causing rendered MKV files to be 1000 fps, no matter what you chose.

Blender VSE is a frame based editor, which means it doesn’t care about the length (in terms of time) of video clips, only the number of frames it has. So if you increase the frame rate, the clips will last shorter. The audio however is time based instead of frame based, so audio clips always play at the same speed, no matter the frame rate.

Your output is playing extremely fast because it’s 1000fps, which is extremely high :slight_smile:
I have no idea why it would include frames you cut out though.


(Skyfish) #3

I made the original videos with audio in OBS, and I set OBS to record and output at 30 FPS, the length of the audio and video did match. edit: starting a new project with my footage, I see it does indeed change to 1000 fps. How on earth did this end up like this? is it because I have a video bitrate of 40000 and audio bitrate of 320, in OBS? I recorded in mkv format. I checked the file in windows file browser too, and it agrees that the video are in 1000FPS so I guess there must be something wrong with OBS.

Edit 2: on further searching, apparantly the 1000FPS thing is a “known bug” with the MKV format, documented here: https://obsproject.com/forum/threads/mkv-files-are-saving-with-a-1000-frames-second.64311/

Is there any way to scale my 1000fps to 30 FPS without having to redo all my work? I heard the time remapping feature might be it, but I don’t understand how it works.
But since the problem stems from the .MKV being incorrectly read, maybe there is something I can do to fix it? as I understand it, the video is actually 30fps but not coded properly? shudder I am going to try and just set the fps to 30, render it and see if it then comes out correctly.

And how come the video looks fine in my preview, audio and video perfectly matched, but when I render it it’s completely off?


(Skyfish) #4

Update: if I change the framerate to 30 and then render, the output video has the correct speed but the audio is misplaced. The preview in blender is also very very slow

Update 2: The cuts in the video seem messed up. This relates back to the question about hard cuts vs soft cuts, there are things in my render that do not show up in the preview and that I specifically cut out.


(3pointEdit) #5

Transcode your mkv to an mp4 file and you should be ok.