In the world of visual communication, it was believed that a higher resolution determined a better video quality. That notion does not quite hold true anymore, after the evolution of the video compression process.
For live video streaming, in particular, the bandwidth is reduced by an exponential margin during the encoding through techniques like spatial image compression or chroma subsampling. This compresses the original raw video to a very easily manageable size.
The correlation between resolution and video quality
The rate of encoding bits in the video is faster in a smaller video as compared to a larger one. Simply speaking, the amount of ‘encoded bits per pixel is higher for a video with lower resolution. What can be easily understood here is that the quality of a live video webcasting is not always better with a higher resolution.
From a test where the same video was encoded at 4Mbps for both 1080p and 720p, the humanly perceived quality of the 720p video was found better than the 1080p. Thus, a lower resolution is preferred for live video streaming. A tool called Video Multi-Method Assessment Fusion (VMSAF) was used to conduct this test. So, even if you are doing HD live streaming, a lower resolution might be better received.
What is HD video quality?
HD refers to High Definition resolution quality of a video. In HD resolution, the pixel height is either 720 pixels or 1080 pixels. Here, 720p is the minimum pixel height to be considered HD, with 1080p to be the maximum. As we know that a higher resolution doesn’t ensure better live video quality; it is possible that your HD live streaming video would look better at 720p rather than 1080p after all.
How to decide the resolution for your live stream?
When you understand the importance of the correct resolution for the quality of your live stream, the next step is about how you decide the resolution. Here are the two main factors to take into consideration:
- Encoding bitrate in your webcasting
- Amount of motion in your live video
It is found that in most cases, 720p videos have better perceptual quality over 1080p videos. While the same results are not found with specific cases that use High-Efficiency Video Coding (HEVC), for a general live video webcasting, the above results hold true.
For your live streaming solutions, the HD resolution need not always be in the higher spectrum of pixel height, rather it would be better to be in the lower spectrum if your viewers do not have higher bandwidths as well.