When someone asks what a video's 'quality' is, there are a number of factors involved.  It's not as simple as 'Full HD' or '4K'.

We get this question quite a lot from customers, so here's our take on the subject.

In our opinion, the quality of a video stream is driven by the following factors:

ResolutionThis is well understood and widely used in marketing.  Common resolutions include:
  • HD - 720p
  • Full HD - 1080p
  • 4K - 2160p
Bit rateThe rate (in bits per second) of data being processed.
This is pretty much the video file size divided by the video duration.
You can find out more in our article Bit rates explained.
CodecThe video codec being used affects the quality because more modern codecs (like H.265/HVEC) will do a better job of preserving the quality of a video than older codecs like H.264.
Apart from the codec being used, there are also the features of the codec itself. H.265 supports High Dynamic Range (HDR) colour and it does this by supporting 10-bit colour encoding.
What this means is, when using HDR, the video stream uses 10 bits to describe the colour of each pixel, rather than 8 bits as commonly used for Standard Dynamic Range (SDR) used in H.264.
A HDR H.265 video will appear to be 'higher quality' than an SDR H.265 video, when viewed on a screen capable of displaying HDR video.
Frame rateA video is really just a bunch of images (frames) displayed quickly one after another.  If you display these images more quickly, the video looks better.

These are the key factors in video stream quality.  The actual quality of the video you see is driven as much by the quality of the screen you're using as the video being played.