Does raising the framerate while not changing the bitrate result in quality loss?

Question

AFAIK, the bitrate is the number of bits *per second*. So let's say I have two videos, both using the same codec, bitrate settings and resolution. If the first one has a framerate of 25fps, but the second one runs at 50fps, does that mean that the second one will have a drastically lower quality since the available bits for each second of the video have to be divided amongst twice as much frames?Or is this effect diminished by motion compensation (e.g. by having more P-frames and less I-frames) or something like that?

Answer 1

Raising the frame rate when shooting while not changing the bitrate will result in a higher frame rate video with less information (data). If you want better quality in the faster frame rate, then raise the bitrate also. Unfortunately, some cameras will not allow a higher bitrate when shooting higher frame rates. In post-production, if you raise the frame rate of a clip on the timeline, it will also lower the quality because the bitrate is already set for the project. If you do a mix down or an export from your timeline you can change the bitrate but the damage has already been done inside your project. So, in answer to your question, raising the frame rate should also be coupled with raising the bitrate (when allowed). If you don't raise the bitrate, the quality difference might not be noticeable to the audience, but it will have less information being processed, so streaming will be easier. I hope this helps.