I know I am doing something wrong because my math does not make sense. Can someone help me explain what am I doing wrong for purposes of learning. This is my logic:

Approach 1

According to the internet 4K video is 233 MB per minute according to this link and others.

If speed is 233 MB per minute this equals

convert to Megabytes per second (233/60)  =  3.9 MB/s
convert to megabites per second           = 31.2 Megabits/s

If this is true this means that if I want to download a 1 hour 4k movie with a internet download speed of 31.2 Megabits/s it will take 1 hour to download?

Approach 2

I have a 4k video on my computer that lasts 28 seconds. The size of the file is 200 MB. Using this information it means that:

convert to Megabytes per second (200/28) =7.14 MB/s
convert to megabits per second = 57.12 Megabits/s

This means that I need an internet speed of 57 Megabits per second to download a 1 hour 4k movie in one hour?

I have a internet speed of 20 Megabits per second and a 2.x hour 4k movie on netflix downloads in less than one hour. Why is this true?

  • Are you asking about raw video, or H.264 compressed video, or HEVC compressed video, etc.? – user1686 Mar 17 '20 at 18:09
  • I did not know that it was compressed. I just want to understand how it works so the math works – Tono Nam Mar 17 '20 at 18:12
  • Well that's kinda the whole point of compression – to make it smaller than what the math says it would be... – user1686 Mar 17 '20 at 18:13

The bitrate of any particular stream depends on the company doing the streaming and the codec they use.

While h.264 may use 30 to 60Mbps for 4K 60FPS content, it does so while trying to keep very high quality, h.265 and newer compression algorithms may need a lot less. If you are willing to loose some quality you can lower the bitrate a lot.

According to HowToGeek Netflix uses approximately 8Mbps to 16Mbps to stream 4K @ 30 frames per second, and 16Mbps to stream at 60 frames per second. It is all about the codec used and the quality you can live with.

Your math seems correct to me. Blu-ray disks are indeed often encoded at 30Mbps or higher and are capable of storing 4K content.

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