Digital signage devices are often purpose-built with embedded hardware (System on Chip). That means there's no way to upgrade the hardware to get more bang for your buck, so optimizing your content is where the wins are.
Reducing the bitrate of content can both preserve the image quality in the video and reduce the overall file size. This is great for Progressive Web App, (PWA) devices, and devices that do not cache content and only stream. By managing the bitrate you can reduce your overall bandwidth consumption on those devices.
For the purpose of this exercise I will be targeting a 1920x1080 video at 30fps. Afterwards I will do the same with a 3840x1080 (Landscape, dual 1080p screen) video at 30fps for Video Wall applications. Lastly I’ll perform the same calculations for standard 4K, 3840x2160. The Codec we will be using is H.264 (MP4).
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Calculating the optimal bitrate for a video isn't a one-size-fits-all number. It depends heavily on the resolution, frame rate, the complexity of the motion in your video, and the codec you are using. You can calculate a highly accurate baseline using the Bits Per Pixel (BPP) method.
The Standard Bitrate Formula
To find your target video bitrate in bits per second (bps), you multiply your total pixel count by your frame rate, and then multiply that by a target BPP value.
Target Bitrate (bps) = (Width) X (Height) X (FPS) X (BPP)
The Bits Per Pixel (BPP) value is variably based on the amount of motion graphics within the Video you wish to encode.
1. Low Motion (0.05 - 0.07 BPP)
2. Medium Motion (0.07 - 0.10 BPP)
3. High Motion (0.10 - 0.15 BPP)
Low motion is your talking-head corporate updates or static graphics. Medium is most marketing content with moderate cuts and movement. High motion is sports, action, or fast-cut promotional reels.
For these examples, I’ll be assuming the video has a medium amount of motion graphics. We will be multiplying the final Pixels Per Second (PPS) value by 0.1. This will provide us the expected Bits Per Second.
For a standard 1920x1080 video at 30fps we achieve 62,208,000.
1920 X 1080 X 30 = 62,208,000 ( pixels per second )
62,208,000 X 0.1 is 6,220,800 Bits Per Second . Typically bitrate is valued in kbps or Kilobits per second. So this calculation result is estimated at ~6200kbps which is the ideal average bitrate for a medium motion video. 6,200 kbps = 6.2 Mbps
For 3840x1080 Landscape video wall we use the same formula with new variables.
3840 X 1080 X 30 = 124,416,000 (pixels per second)
124,416,000 pixels per second would roughly be equal to 12,441,600 bits per second for medium motion graphics. This equates to ~12,400 kbps.
Now for Standard 4K, 3840x2160 at 30fps this will be double the bitrate as the last calculation, or four times the size of standard 1080p.
3840 X 2160 X 30 = 248,832,000 (pixels per second)
248,832,000 pixels per second would net out to be ~24,883,200 Bits per second or roughly ~24,800 kbps or ~25,000 kbps for medium motion graphics.
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Now please keep in mind a few things as we wrap up.
Firstly, this guide has not taken into account Audio for the videos, if you do have Audio within them you just need to add usually around 128 kbps to 192 kbps for standard signage.
H.264 is widely supported but is an older codec. H.265 / HEVC is also widely supported by many different device models and can have up to 40% shaved off the final bitrate value while still maintaining the image fidelity you would expect from high bitrate video content.
Not all devices will perform the same. This guide is to help you find the ideal bitrate for your Signage Solutions. We always advise testing your content prior to production deployment to avoid issues.
Lastly, HandBrake and FFmpeg are free utilities you can use to re-encode your video content as needed. Both are free, open-source software available on the web. https://handbrake.fr/ https://www.ffmpeg.org/
Kind regards,
Ken Jeter
Strategic Account Manager
Appspace.com