Need help understanding file sizes

[pieNICE]

Hello!

I usually record some gameplay and resulting file size is OK. It usually takes 2-10GB/hour for HD 60 fps 2500 Kbpsrecording in .mkv. While I don't understand why some games in recording take more place then others, I think it's normal.

But recently I started recording camera footage. I use two cams: one is 240*320 and another is 720*1280. I create another scene for them and then resize them a bit so the would fit into 1080*1920 recording. And for some reason those shitty cameras somehow make recordings 10GB/hour at least?? Like recording from my phone that is 1920*1080 too is 3 GB/hour maximum! Why recording from PC is this huge T_T

Can somebody explain, please, is this normal or I f-ed up something?

 

[koala]

If a recording is 2500 kbps, it's 2500 kbps regardless the resolution, the fps or whatever. It's 2500 kbit per second. So it's 2500/8 = 312.5 kbyte per second or 312.5*3600 = 1125000 kbyte per hour = 1.125 GB per hour.

In case you record with a quality based rate control such as cqp, icq or crf you don't record with a fixed bitrate as in CBR mode with 2500. Instead it depends on the quality that is requested. The more quality requested, the larger the dynamic bitrate. Also motion is a factor in this mode: low motion video requires much less dynamic bitrate than high motion video. Finally resolution and fps also are a factor: double the resolution means 4 times the amount of pixels, so 4 times the file size. Doubling the fps doubles the data, so it's 2 times the file size.

If you record with your phone, the phone usually encodes with a constant somewhat low bitrate, so the resulting video is rather small. If you use OBS for recording and use a quality based preset, it will use much more bitrate so the resulting file is much larger. It's way better quality, if you compare videos side by side. Good quality needs file size.