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Compression with a static image within a video

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Max PalmerCompression with a static image within a video
by on Mar 23, 2016 at 5:24:07 am

Hi guys!

Long time user of this forum, although this is the first time I haven't been able to find the answer I've been looking for! So thanks for all the previous answers I've found :)

Basically...

I'm creating a video header for my new website. I've had a graphic designer draw me a TV, and my videos will appear within this TV. I've made the header video in Premiere with the still TV image as a layer above the video.

All reasonable logic tells me that if a static image (i.e. the TV) occupies most of the video, and the only moving parts are the video within the TV, then the file size of this rendered video should be much smaller than say a 1080p video that is 100% video, with no still images.

However, I have found that this is not the case. I would presume that the renderer would only have to render the static image once, for one frame, and that data could be used for all the remaining frames. However, it seems that it is rendering each frame individually even though 50% of the frame isn't changing. This results with the still image within the video fluctuating in quality in accordance to the activity within the actual moving video. This is obviously not desirable.

There is a very draft example on my site at the moment if it helps to have a look -
http://www.maxpalmervisuals.com
Password - fables

I'm using Premiere's built in h.264 compressor. The file format has to be .mp4. Should I be using a different rendering engine? Should I use Premiere's 'image overlay' function in the rendering window, rather than having the image in my timeline?

What it somewhat boils down to is, if I had a static image, and had nothing but this in a video, with no movement or anything, then logic suggests that video should remain the same file size no matter how long it is. Right?!

I would be grateful if someone has the answer to this question, as I don't really wanna keep rendering 10000 different versions!

Thanks very much :)


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Pierpaolo FerlainoRe: Compression with a static image within a video
by on Mar 23, 2016 at 10:28:24 am

I'm on a tablet at a the moment and for some reason I can't see the video header on you website but according to what you are writing you're starting from wrong assumptions...
Data rate is measured in bps which is byte per seconds: that means duration really cares... It doesn't matter if you're using a static or a moving image...
If you're using cbr compression 30 seconds of static image will be equal to 30 seconds of moving image.
If you use vbr compression 30 seconds of a static image will be smaller than 30 seconds of a moving image but 35 seconds of a static image will be greater than 30 seconds of the same static image.

In a movie with mixed static and moving images vbr compressioon will result in frames which are more or less compressed according to the complexity of the scene.

That said, it's weird you see visual difference in the static image (the tv) and it's probably a matter of compression settings... maybe you're using a data rate which is too low...


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Max PalmerRe: Compression with a static image within a video
by on Mar 23, 2016 at 10:44:40 am

Ah yeah I haven't got it set up to work on mobile yet. I think the video header only works on Chrome on desktop at the moment.

Thanks for your input. I'm compressing at a mere 2.5mbps, but I think that is even too high - I don't want it to lag.

Surely in this day & age there must be a compression technology that will realise "this image isn't changing - I don't need to re-render that 25 times a second"... Surely!


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Duke SwedenRe: Compression with a static image within a video
by on Mar 23, 2016 at 1:05:15 pm

I just watched it and there is absolutely NO fluctuation in the quality of the static image. Looks fine from here.

Aside from that, I don't do client work, I'm basically a hobbyist, and most of my videos involve green screen with a static background. In my test renders I see no difference in file size from my final renders including the background image. So, take it for what it's worth. Pierpaolo more or less gave you the technical reasons.


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Andrew KimeryRe: Compression with a static image within a video
by on Mar 23, 2016 at 4:29:56 pm

I'm running the most recent version of Chrome on a Mac and I'm not seeing any image quality fluctuations.


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Alex UdellRe: Compression with a static image within a video
by on Mar 23, 2016 at 7:50:13 pm

Hi...

Can you do the web design frame as an element with alpha on top of the video player?

Instead of including it in the video render itself?

CSS and Z-index







then as long as you know the aspect ratio you can cheat and render the video at 50% size but set the video player properties to 200%

that will make your video fill the frame and the filesize would be smaller.

Alex Udell
Editing, Motion Graphics, and Visual FX
Let's Connect on Linkedin
Examples: Retail Automotive Motion Graphics Spots
Example: Customer Facing Explainer Video
Example: Infotainment & Package editorial


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Max PalmerRe: Compression with a static image within a video
by on Mar 23, 2016 at 10:23:52 pm

Hey, thanks for all the replies, appreciate it.

I'm glad that some of you haven't noticed the image quality fluctuation - maybe I'm being too much of a perfectionist!

Alex, I did think about doing that. I'm not too savvy with web coding but I will give it a go!

Thanks again for the help :)


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