720p video recording at same bitrate as 1080p video.

[ShadowWizard]

I am kinda new to the world of video, at least anything beyond basic recording/storing, so please mind me.
I have an action cam. Its called an Elecam, I am not sure what version/model off the top of my head, but I am not sure it matters. I recently switched my video recording from 1080p/60fps to 720p/60fps to try and save some space, but noticed that the videos are the same size! Its set to cut each video at 15 min, and there all about 3.3gb. Both the 1080 and 720 I checked the bitrate, and they are both about the same at 31500 or so. Any ideas whats going on? Shouldn't the 720p videos be smaller?
-edit-
It is an elecam explorer

[davexnet]

Check the specs of your camera. Perhaps it's using a constant bitrate

[ShadowWizard]

Would it be constant if I am getting a different bitrate with each video? For example one is 31569 and another is 31422?
And are you suggesting that the camera has a setting to change the bitrate (can't find it) or that the bitrate is constant and doesn't change.. If that second question is even still applicable after the first bit of information.

[davexnet]

I'm not suggesting anything, that's why I suggested looking up the specs of the camera and
see what you can find out.
If you find a low demand scene produces a file with a much lower bitrate,
then the constant rate is obviously wrong, more likely using some kind of constant rate factor or similar.

There are others on the forum who can give more details that I. You should at least provide
the exact camera model

[ShadowWizard]

So, I edited my post after I found the model number, plus did some more testing. I recorded nothing but black for 10 seconds. The file is 2.3 megs, and says it has a bit rate of 987kbps.
I then recorded a part of the room I am in for 10 seconds, add the video is 42 megs, and says it has a bit rate of 30538kbps. I am guessing this means it has a variable bitrate?

[jagabo]

Shouldn't the 720p videos be smaller?

file size = bitrate * running time

Resolution doesn't enter the equation. In general, the higher the resolution the more bitrate you need to keep the video from degrading. But apparently you camera uses the same bitrate for 720p and 1080p. That should mean the 720p videos are less degraded but at high bitrates like 31500 (h.264?) the quality may be high enough that you can't tell.

[ShadowWizard]

Yes, it uses h.264. So I think I am understanding. Bitrate is a separate setting. You can technically record 480p video at a stupid high bitrate then and get file sizes bigger then the 1080p that I am getting. hmm, so I am wondering what the point is to have the setting in the camrea? To choose between 1080p and 720p I mean.

[jagabo]

I am wondering what the point is to have the setting in the camrea? To choose between 1080p and 720p I mean.

A higher resolution can give a sharper picture as long as it isn't over-compressed or otherwise mistreated. Some video is more easily compressed than others. High motion, lots of noise, flickering lights, billowing fog -- things like that make video hard to compress because high compression codecs get most of their compression by not repeating parts of the frame that don't change from frame to frame. So a clean still shot of a bowl of fruit will compress much better than a misty waterfall, or a closeup of a tree with all it's leaves wiggling about with the wind.

[ShadowWizard]

Okay, I think I understand a bit better now. Thanks.