Video compression- how to prioritize one area over another?

Question

I'm not sure if what I'm asking is possible, but here's the situation.

I have a video I have made for distribution on the Internet (YouTube, Vimeo, etc.)

The video clip is a composite of the following:

• a person talking (shot against a green screen)
• a city scene in a harbor at night; the bottom half of the frame is filled with moving water (the ocean)

So, when I compress this using standard settings, the waves are given the most detail (because they move the most?), and the person shows more compression artifacts.

However, ideally, I want the person to be kept in the highest possible detail, and the water to be compressed more.

The compressor itself doesn't have any settings for something like this, but since the clip is a composite, I was thinking there might be a way to compress the layers separately... Can this kind of thing be done?

I'm using Davinci Resolve but I also have access to FCPX.

Answer 1

This is an interesting question, but I don't think that you will find a good solution without changing your inputs (the video elements you are using). I'm not aware of any software that allows you to prioritize compression by area. The compressor itself usually makes all these kinds of decisions for you.

Aside from that, you said the magic (not good) word for compression: Youtube. Even if you could find a way to do the above, you basically give it all up when you upload it to Youtube, where they will run their own fixed compression algorithms that will ruin all your work.

I think there are a couple of things you can do (perhaps all of them in combination):

1. If you haven't already, try doing 2-pass compression, instead of one-pass. This will take longer, but the compressor will have a chance to analyze the video on the first pass, and that may possibly help improve your output a little.

2. Massage that water footage. If you can get rid of it completely and replace it with something else that causes less trouble, do it. If not, you can try things like:

   • Apply some blur (either chroma [color portion of the signal], luma [monochrome portion of the signal] or both) to the footage.

   • It would also help to run the water footage through a denoiser first.

Both denoising and slight blurring should help reduce the amount of bandwidth that your compressor needs to dedicate to that area of your video.