Codec Guide
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Understanding how codec works.

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Understanding how codec works. Empty Understanding how codec works.

Post by Spykel on Thu Mar 12, 2020 11:42 am

Hello!

I'm new in the codification world, and I think that after reading a lot of information, I need some clarifications.

Let me explain my doubts:

Current iPhones, when you record on 1080 30fps, it creates a .mov (container) with h264 (codec). I have tried to record a static video of 1 minute, and then another video of 1 minute but with movement.

I thought, that the second one would be heaver (in size terms) than the first one, but to my surprise, both videos have the same size...

Also, I thought the second one would have more keyframes (since the first one, can create more predictive frames because all is the same)... But they both have the same amount of I-frames (and same GOP).


Why happens this? The iPhone's encoder, does not change in every situation?

Sincerely,
Spykel

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Post by Admin on Thu Mar 12, 2020 3:01 pm

It uses a hardware based encoder, which are usually rather limited in configuration and complexity compared to a software based encoder. But more importantly, encoding is done in realtime, so it can't analyze the video first to potentially optimize parameters.

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Post by Spykel on Thu Mar 12, 2020 3:31 pm

First of all, thanks for answer.

I have been looking a little bit about "hardware-based encoder" and "software-based encoder".

Taking in account what you have said, it means that is normal to not get "any" difference between a video where every frame is the same.. and a video with a lot of movement.

So if I have understood it well.. If you want to get good results in this case.. You should record it without any kind of compression, and then add "manually" a software-based encoded.

Sincerely,
Spykel

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Post by Admin on Thu Mar 12, 2020 3:50 pm

A video with less movement theoretically requires less bits to encode given a certain quality as target. But it is possible that the encoder uses a constant bitrate. In that case the video with less movement can have better visual quality.

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