You didn't mention what resolution/frame rate you're using, but H264 at 8Mbps seems really low, especially for something like sports where there's constant motion. I probably wouldn't go below 32Mbps for 1080p60.

This isn't something like a talk show where they're just sitting at a desk and barely moving.

Maybe try switching to HEVC and also bumping that 8 to something larger.

But no matter what you do, until you hit a certain point, your quality will be proportional to your file size. Even with the most efficient codec, the file can only get so small before you start running into problems like you're describing.

I don't work for vMix, I'm only posting my guess as to what is going on, and why you are seeing different results.

I bet the difference is OBS is probably using variable bitrate, and when you set 8Mbps, that's the average, and it is allowed to jump up higher than that for certain scenes (lots of motion or transitions).

I bet vMix is using constant bitrate, or possibly variable bitrate, but the 8Mbps is probably a hard cap. So even if you set 8Mbps on both, I bet the resulting file size on vMix is probably smaller. If you raise the bitrate in vMix to give you similar filesize as what you would get in OBS, the bitrate number might be higher (who cares, it's just a number) but the filesize is similar and probably has similar quality.

I don't know for certain, but that's probably what's going on. I would do some experiments and see if vMix is actually making similar file sizes when you set both to 8Mbps.

-- Kevin