A while ago I rendered out a video at 1080p and then again at 720p.
As expected the 720p file size was considerably smaller than the 1080p one. However I thought I’d play a bit more with this as I was a little ‘uncertain’ with the results I was getting, after all not just image size (1080 / 720) had changed, but bit rate too. On play back both videos looked ‘good quality’ and even stretching the 720 up to fill a 1080 size window didn’t noticeably reduce its viewing quality.
So I took a short 20 second clip standing on a street corner which started with the camera held still (so a mix of non-moving buildings but with cars and people going past) and then at the 10 second point panned the camera around so everything was now moving relative to the camera.
Then it was a case of rendering this out at 1080p various times, the only thing being changed between each session being the bit rate, working up from around 800 Kbps to 32Mbps.
Down at the low bit rates stationary items looked all right, but moving items (people, cars, the buildings when the camera was panning around) were of very poor quality. At the high bit rate end of the scale everything looked crisp and nice, however both rendering time and file size had also grown.
What was also apparent was that the choice of playback program was significant. Different players, VLC, Windows Media Player, QuickTime, all will play back the same clip differently. Same applies to using different browsers as a play-back engine – they are not all equal. Also what you have recorded makes a difference. A clip with little movement and few colours will be very different from a clip with lots of movement and activity.
Then a matter of working up from the bottom to find the bit rate cut-off point between where a clip was unacceptable and one was watchable; and coming down from the high bit rates and at what stage starting to notice a degradation in quality. Then finding an overall mid-point balance between quality and file size .
So what this really means is that there is no one ideal bit rate setting that’s going to cover all situations. For my set-up, with my camera and my editing software and thinking of uploading to somewhere like Vimeo or YouTube, then I’ll be thinking of working at 8 Mbps for indoor videos where there’s not a lot going on, and 12Mbps for outdoor videos full of colour and movement.
But this just my experience. You will need to do your own experiments to find your best compromise settings that will suite your equipment and set-up.