Bitrate on CBR vs VBR vs FPS v H265

R

Robert de la Vega

n3wb
Jan 6, 2018
7
2
If the default setting of the camera is H264 20fps CBR 4096kbs will I get about the same quality if I set it to H265 10fps VBR 2094?

Does FPS correspond 1:1 with bitrate... Is 4096 @ 20fps the same exact quality as 10fps @ 2048? If not what setting would be idea to keep about the same quality as default but lower the storage space? Also is it really true that with H265 I get better quality per bitrate vs H264?
 
It is not exactly 1:1 because iframes, which typically come once every 1-3 seconds regardless of your frame rate, take up an extra-large slice of the bit rate pie. So I believe to get equivalent quality at half the frame rate, you would need somewhat more than half the bit rate.
 
VBR encoding is basically "constant quality", limited by whatever bit rate you set. If the encoder can achieve your set quality level with a lower bit rate than your bit rate setting, then it will do that, and you will save some data. I would suggest you enable VBR, max out the bit rate setting, and then play around with different quality levels and frame rates to see what the bit rates end up being (of course you'll need a convenient way to measure the actual produced bit rate. Perhaps your camera's web interface will tell you). This will give you a better idea of how much bit rate you can save by reducing FPS without sacrificing image quality.
 
One experiment you could run is:

1) Set the video encoding settings to VBR, 20 FPS, max bit rate.
2) Play with different quality settings and monitor the actual bit rates of the stream. Choose the quality setting that gets closest to approximately 4096 Kbps output. (If you don't have a better way to measure the resulting bit rate, VLC media player can show you the bit rate in the Current Media Information panel, statistics tab.)
3) Reduce FPS to 10 and take note of how much the bit rate went down -- that indicates how much you can save without reducing image quality.
 
Robert de la Vega said:
Also is it really true that with H265 I get better quality per bitrate vs H264?
Click to expand...

Yes, h.265 also known as HEVC is a much more efficient codec. It was designed for 4k video to deal with the potentially enormous amounts of data it produces. h.265 produces roughly half the compressed file size of h.264 for the same or better quality.
 
Since we're here, could someone discuss the bitrate impact of H.265 versus the Dahua's H.264H ?
 
@bp2008 I like the way you separated your well thought out replies to the various sub-questions.

Doesn't SmartPSS display the accurate second by second bit rate in the live view field? I would think that would be the easiest way to look at the tweaks, as it is also the tool to make the adjustments.

I suspect that you will see a medium to small change in bit rate from 20 fps to 10 fps (but you will see it), due to I frames. I use 10. (don't confuse frame rate with shutter speed)
I suspect that the more pixels in frame (12MP vs 2 MP) the larger the change from H265 to H264, but i would like to see real data (same screen various camera resolutions and the two compression codes). This could be a fairly large change even with a 2MP.

As we all know, it depends a lot on the activity in the frame. A static well lit hallway is way different than an active road with bushes and trees.
 
You must log in or register to reply here.
Top Bottom