Different decode performance in two similar H.264 videos

Question

I have two, at first glance very similar mp4 files (A & B), each of them created by different capture software.

File	Captured using	codec	resolution	fps	bitrate
A.mp4	Elgato 4K Capture Utility	h.264	2560x1440	60	106Mb/s
B.mp4	Xsplit Broadcaster	h.264	2560x1440	60	128Mb/s

I noticed that scrubbing video A is very smooth while scrubbing video B is extremely choppy.

This video illustrates the difference. Note that althought for demonstration purpose I've used DaVinci Resolve software, the same scrubbing performance is present in other programs e.g. VLC Player.

I would like to understand what is causing this difference in scrubbing performance. Looking at task manager graphs, it seems like video B is more complex to decode but I have no idea why.

This is what I got using MediaInfo

Answer 1

Figured it out. The difference in scrubbing performance comes from different GOP in those two videos. The video which played smoothly had GOP=(N, M)=(15, 1).

So for people who'll encounter this issue in videos produced by their capture software: to fix it set keyframe interval to low value e.g. 30 frames (0.5sec)

It's also possible to convert existing videos using ffmpeg in order to add more keyframes e.g.

ffmpeg -i input.mp4 -c:v libx264 -crf 16 -preset faster -g 15 output.mp4

where -g 15 sets keyframe every 15 frames