Hello Fellow Yuneec Pilot!
Join our free Yuneec community and remove this annoying banner!
Sign up

Video Bit Rate Question

Joined
Aug 1, 2016
Messages
931
Reaction score
307
Location
Auburn, WA, USA
I'll bet someone out there knows the answer.
Yesterday I did some testing with the CGO3+ at various resolutions and frame rates and exposures and shutter speeds. What I found was totally unexpected. I understand how the video bit rate is effected by the resolution and frame rate. But what I discovered was that the video bit rate was also effected by the ISO and shutter speed. Here's some data:
  1. 1920x1080x60, ISO 100, shutter 1/60: Bit rate 20 Mbps
  2. 1920x1080x60, ISO 100, shutter 1/125: Bit rate 29 Mbps
  3. 1920x1080x60, ISO 100, shutter 1/250: Bit rate 32 Mbps
  4. 1920x1080x60, ISO 400, shutter 1/125: Bit rate 50 Mbps
  5. 3480x2160x30, Auto, EV -0.5: Bit rate 50 Mbps
  6. 4096x2160x24, Auto: Bit rate 50 Mbps
Notice the nice trend in the first 3 data points at ISO 100. I see a lot more detail in the 50 Mbps video (#4) vs. the 20 Mbps video (#1) even though the resolution and frame rate are the same. What's going on here? Why do ISO and shutter speed impact bit rate?
 
Joined
Sep 13, 2016
Messages
164
Reaction score
57
Age
27
My guess would be it's to do with the compression algorithm. With a slower shutter speed there is more motion blur (a sort of smearing across frames). The compression algorithm will find this much easier to encode as a lot of pixels are similar between the frames due to this 'blur'. As the shutter speed increases, this blur reduces so the information it needs to encode becomes more different frame to frame and the encoder can't compress the data rate as much whilst still retaining detail.

As you increase the ISO, the amount of noise increases in each frame. As this noise is random it can't be encoded efficiently, so the encoder needs to use a higher bitrate to not lose the detail.

I am not a video expert (I'm actually an audio expert with some knowledge on audio/video encoders), but this kind of makes sense logically to me as to how I know encoders work.
 
  • Like
Reactions: Eagle's Eye Video

CraigCam

Premium Pilot
Joined
Oct 1, 2016
Messages
1,515
Reaction score
647
Age
60
If you add an ND filter these numbers change as well. The ideal target in daylight is The lowest ISO setting of 100 and shutter speed double the frame rate. I use ND4 or ND8 Polar Pro filters to get these numbers working and then I can adjust EVO to get my histogram leaning towards under exposed if possible. Auto mode color corrects too much but you do want that on when you first initialize the camera. Once booted, lock the White Balance, then go into your ISO and shutter speed to adjust accordingly. Not sure why you had a 400 over 125 going but yes that will yield better results as you doubled the shutter speed relative to frame rate.

Don’t forget, resolution of video is very monitor dependent to objectively judge. When 4K screens drop some more, I’m looking forward to seeing what the 4K on the CGO3 + is really like. It’s very hard to judge when refresh rates on screens can’t keep up with the video output.
 
Joined
Jun 9, 2016
Messages
1,480
Reaction score
1,297
Age
49
Location
UK
The video compression is variable rate - meaning it will use more or less data depending on how much detail and movement there is in the video. The rate changes constantly during a video, so it can be low at one point and high at another. When you use software that reports a single bitrate for a whole video, it's just taking the average of the different rates.

You can test this out by pointing the camera at a still scene (you'll see low bit rate) and then moving it around a lot (high bit rate). When you change the ISO and shutter speed you will change the amount of detail and noise in the picture, which will change the bit rate as @samsflite correctly says.
 
Joined
Aug 1, 2016
Messages
931
Reaction score
307
Location
Auburn, WA, USA
If you add an ND filter these numbers change as well.
Not sure why you had a 400 over 125 going but yes that will yield better results as you doubled the shutter speed relative to frame rate.
Don’t forget, resolution of video is very monitor dependent to objectively judge. When 4K screens drop some more, I’m looking forward to seeing what the 4K on the CGO3 + is really like. It’s very hard to judge when refresh rates on screens can’t keep up with the video output.
I was wondering if anyone would notice. Yes, I used ND8 for the ISO 400 at 1/125 video. The filter has an indirect effect on bit rate by changing the ISO and shutter speed.
My 4K monitor is great for critically evaluating photos and videos. Mine is Dell P2415Q that cost $380 one year ago. I enjoy watching 4K 30p and 60p YouTube videos as well as my own 4K videos.
Thanks for the thoughtful response.
 

New Threads

Forum statistics

Threads
16,640
Messages
193,985
Members
19,311
Latest member
Carmel