keyframe interval and max b-frames for high FPS recordings

[r_ad]

Hey everyone! I'm trying to perfect my obs settings as best as a can and so far it's been going well. I understand most terminology but two settings that I don't really understand very well are "keyframe interval" and "max b frames." It seems like most people recommend leaving both settings at the value of 2 but I'm in a bit of a pickle because I record at a very high fps. Since both of these settings are FPS-related, and most people record at 60 frames per second, it seems like this default value doesn't apply to me. I record at 240 FPS and render at 60 FPS in VEGAS Pro 19 using smart resample and frame blending to give the video a sort of motion blur. If someone could help me understand these settings and how they apply to me that would be great! Thank you!

 

[rockbottom]

2x4=8

0

 

[rockbottom]

Test both, B frames make the recordings soft to my eyes. No more than 2 if you use them.

I do some if not all of my editing with Avidemux before Vegas, so I insert a keyframe every half second. Avidemux works best when cutting on a Keyframe.

 

[rockbottom]

In case you don't have this installed for Vegas.

The Powerful and Free Media Encoding Plugin - Voukoder

www.voukoder.org

 

[koala]

The two parameters deal with quality. They trade off space for quality. If you record with a quality-based rate control such as CQP or CRF, you have infinite space, so you can just optimize for quality if you want. B-frames are the ones with the highest compression (most detail removed), so the more B-frames you insert, the lower the quality. So to optimize B frames for quality, you should use 0 B-frames (none at all) with CQP.
With key frames, it's the same, only on a higher level and the other way round. They contain a whole frame and are an anchor for P-frames, which have a higher higher compression (less detail removed) than the keyframes (but lower than the B-frames). So if you want higher quality, use more keyframes, which can be achieved by using a smaller keyframe interval. It has the side effect that a video with more keyframes is better seekable. With lower keyframe interval, video size increases vastly.

With CBR rate control, the effect is reversed, since you limit the bitrate. To achieve the forced bitrate, the encoder removes as much detail as needed. If you don't use B-frames or use a lower keyframe interval, the bitrate is consumed completely by the bigger frames, so the general quality must be lowered, which is very visible. So don't do this (don't use CBR for recording).

 

[r_ad]

The two parameters deal with quality. They trade off space for quality. If you record with a quality-based rate control such as CQP or CRF, you have infinite space, so you can just optimize for quality if you want. B-frames are the ones with the highest compression (most detail removed), so the more B-frames you insert, the lower the quality. So to optimize B frames for quality, you should use 0 B-frames (none at all) with CQP.
With key frames, it's the same, only on a higher level and the other way round. They contain a whole frame and are an anchor for P-frames, which have a higher higher compression (less detail removed) than the keyframes (but lower than the B-frames). So if you want higher quality, use more keyframes, which can be achieved by using a smaller keyframe interval. It has the side effect that a video with more keyframes is better seekable. With lower keyframe interval, video size increases vastly.

With CBR rate control, the effect is reversed, since you limit the bitrate. To achieve the forced bitrate, the encoder removes as much detail as needed. If you don't use B-frames or use a lower keyframe interval, the bitrate is consumed completely by the bigger frames, so the general quality must be lowered, which is very visible. So don't do this (don't use CBR for recording).

ur actually a genius

 

[r_ad]

do u have any recommendations for my keyframe interval? keep in mind i record at 240 fps

 

[rockbottom]

With the Simple/Standard outputs the interval is set in seconds (not frames) so 1 or 2 max. 1 will insert a Keyframe every 240 frames, 2 every 480 frames. If you decide you want to insert a Keyframe more often, like every 1/2 second (120 Frames) or 1/4 second (60 Frames) you'll need to learn how to use the Custom FFMPEG Output.

 

[r_ad]

With the Simple/Standard outputs the interval is set in seconds (not frames) so 1 or 2 max. 1 will insert a Keyframe every 240 frames, 2 every 480 frames. If you decide you want to insert a Keyframe more often, like every 1/2 second (120 Frames) or 1/4 second (60 Frames) you'll need to learn how to use the Custom FFMPEG Output.

thank u