Latest revision: 2022-09-18
What is the spoRv Gauge™?
It’s a rule of thumb to calculate the optimal bitrate needed to encode a good quality video – or to check if a given video reach a good quality level; it is based on the Kush Gauge, an original formula invented by Kush Amerasinghe, a computer scientist. In this context, the word “gauge” means “a device used to make measurements“
How does it work?
To estimate the optimal bitrate value that would give what is considered “good quality” results for a given video, you could multiply the frame resolution by the frame rate; then multiply the result by its motion rank factor; then multiply the result by codec constant; then multiply the result by the chroma subsampling factor; then multiply the result by the bit depth factor; then multiply the result by grain factor; then multiply the result by scan mode factor, to get the bit rate in bps – divide that by 1,000 to get a kbps estimate or by 1,000,000 to get a Mbps estimate.
spoRv Gauge aim to expand the original formula – that was limited to only one codec, one chroma subsampling, one bit depth, one scan mode – to more factors, so that can be used with several codecs, different chroma subsamplings, bit depths, scan modes; it adds also grain factor.
The spoRv Gauge™ formula:
codec constant ✕ resolution ✕ super resolution ✕ frame rate ✕ scan mode
✕ chroma subsampling ✕ bit depth ✕ grain ✕ dynamic range ✕ motion rank
= optimal bitrate
codec x265, 1920×1080 2.20:1 source = 1920×872 = 1674240 pixels, 24 frames per second, interlaced, 4:2:2, 10bit, standard dynamic range, with grain, motion rank high
0.0430 ✕ 1674240 ✕ 1 ✕ 24 ✕ 1.2 ✕ 4/3 ✕ 1.25 ✕ 1 ✕ 1.5 ✕ 4= 20733788bps = ~20.8mbps
What are the codec constants?
The codec constants are set as follow:
- AOMedia AV1
0.0465 (SD) ― 0.0407 (720p) ― 0.0342 (1080p) ― 0.0174 (2160p) ― 0.0123 (4320p)
- Google VP9
0.0616 (SD) ― 0.0481 (720p) ― 0.0388 (1080p) ― 0.0213 (2160p) ― 0.0168 (4320p)
- h.266 | VVC
0.0403 (SD) ― 0.0315 (720p) ― 0.0254 (1080p) ― 0.0155 (2160p) ― 0.0110 (4320p)
- h.265 | HEVC
0.0683 (SD) ― 0.0534 (720p) ― 0.0430 (1080p) ― 0.0263 (2160p) ― 0.0186 (4320p)
- h.264 | AVC
0.0980 (SD) ― 0.0840 (720p) ― 0.0700 (1080p) ― 0.0495 (2160p) ― 0.0350 (4320p)
- h.264 | MVC
0.1575 (SD) ― 0.1350 (720p) ― 0.1125 (1080p) ― 0.0796 (2160p) ― 0.0563 (4320p)
- h.263 | MPEG-4 part 2
0.1260 (SD) ― 0.1080 (720p) ― 0.0900 (1080p) ― 0.0637 (2160p) ― 0.0450 (4320p)
- h.262 | MPEG-2 (hardware encoder)
0.1624 (SD) ― 0.1392 (720p) ― 0.1160 (1080p) ― 0.0821 (2160p) ― 0.0580 (4320p)
- h.262 | MPEG-2 (software encoder)
0.1904 (SD) ― 0.1632 (720p) ― 0.1360 (1080p) ― 0.0962 (2160p) ― 0.0680 (4320p)
- h.261 | MPEG-1
0.2002 (SD) ― 0.1716 (720p) ― 0.1430 (1080p) ― 0.1012 (2160p) ― 0.0715 (4320p)
- VC-1 | WMV3
0.1050 (SD) ― 0.0900 (720p) ― 0.0750 (1080p) ― 0.0531 (2160p) ― 0.0375 (4320p)
What is resolution?
It is the frame resolution in pixel – width ✕ height
What is Super Resolution?
It’s an algorithm that, when used, allows the input video pictures to be coded at a lower resolution and then upscaled to the original resolution after reconstruction; the downscaling factor is applied to the horizontal direction only, and is constrained to 8/9 ~ 8/16, i.e, maximum 2x.
What is frame rate?
It means how many frames are shown each second.
What are the scan mode factors?
The scan mode factors are set as follow:
- 1.0 for progressive video
- 1.2 for interlaced video
What are the chroma subsampling factors?
The chroma subsampling factors are set as follow:
- 3/3 for 4:2:0
- 4/3 for 4:2:2
- 6/3 for 4:4:4
What are the bit depth factors?
The bit depth factors are set as follow:
- 1.00 for 8 bit
- 1.25 for 10 bit
- 1.50 for 12 bit
- 2.00 for 16 bit
What are the grain factors?
The grain factors are set as follow:
- 1.00 for source without grain or using grain synthesis
- 1.50 for source with grain
What is Grain Synthesis?
The grain synthesis algorithm denoises the input video pictures, and then the resulting denoised version are used in the encoding process. In the second step, a model of the film grain in the source picture is estimated at the encoder side, and the noise model parameters are included in the bit stream for the decoder to reproduce the noise and add it in the reconstructed pictures.
What are the dynamic range factors?
The dynamic range factors are set as follow:
- 1.00 for SDR, HLG, HDR10, HDR10+
- 1.25 for Dolby Vision
What are the motion rank factors?
The amount of motion could be called “motion rank”; let’s see some examples:
- 1 – low – a person talking in front of a camera without moving much while the camera itself and the background is not moving at all
- 2 – medium – some degree of movement, but in a more predictable and orderly manner, which means some relatively slow camera and subject movements, but not many scene changes
- 3 – high – an action movie where the movements are fast and unpredictable but with not many scene changes or cuts or sudden snap camera movements or zooms where the entire picture changes
- 4 – highest – the most challenging action movie where not only the movements are fast and unpredictable but the scenes also change very rapidly
WOW! A quite complicated formula…
A bit! To find out the optimal bitrate – or to check if any video was encoded with a sufficient bitrate to get good quality – and also to check format compliance, you can always use the spoRv Gauge calculator!
- spoRv Corollaries to the Kush Gauge
- The Kush Gauge – H.264 FOR THE REST OF US (page 21)
- power of 0.75” rule
- SUBJECTIVE QUALITY ASSESSMENT OF THE EMERGING AVC/H.264 VIDEO CODING STANDARD
- EBU Technical Report 008 – HDTV Contribution Codecs
- Using AVC/H.264 and H.265 expertise to boost MPEG-2 efficiency
- BBC Guidelines – Technical and Delivery Standards for Worldwide
- Comparison of the Coding Efficiency of Video Coding Standards
- Future Performance of Video Codecs
- AVC, HEVC, VP9, AVS2 or AV1? — A Comparative Study of State-of-the-art Video Encoders on 4K Videos
- AV1 Has Arrived: Comparing Codecs from AOMedia, Visionular, and Intel/Netflix
- AV1 vs HEVC: Perceptual Evaluation of Video Encoders
- MSU Video Codecs Comparison 2020 Part 1: FullHD, objective
- Perceptual Quality Assessment of HEVC and VVC Standards for 8K Video