CODEWITHSUNDEEP
youtubecpu-usagedownload
MFM
MFM

Reputation: 91

CPU load of streaming vs file downloading when routing data

I'm using a Raspberry Pi 2 to route wifi-eth connections. So from the eth side I have a computer that will connect to internet using the Pi wifi connection. On the Raspberry I started htop to monitor the CPUs load, then on the computer I started chrome and played a 20-minute 1080 video. The load on the CPU didn't seem to go beyond 5% anyhow. After that I closed youtube tab and started a download of a binary file of 5GB from the first row here (https://testdebit.info/). Well, I noticed that CPU load was much more higher, around 10%! Any explanation of such a difference?

Upvotes: 0

Views: 126

Answers (1)

Taylor Kidd
Taylor Kidd

Reputation: 1511

It has to do with compression and how video is encoded. A normal file can be compressed, but nothing like that of a video stream.

A video stream can achieve very high compressions due to the predictable characteristics of video, e.g. video from one frame to another doesn't change much. As such, video will send a whole frame (I-frame) and then update it with just the changes (P-frame). It's even possible to do backward prediction (B-frame). Here's a wikipedia reference.

Yes, I hear your next unspoken question: Doesn't more compression mean more CPU time to uncompress? That's true for a lot of types of compression, such as that used by zip files. But since raw video is not very information dense over time, you have compression techniques that in essence reduce the amount of data you send with very little CPU usage.

I hope this helps.

Upvotes: 1

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