Running video behind fixed image.

[D138]

Hey. New to this so apologies if it's a straight forward matter.

I'm using the image below just for illustrative purposes.



My questions is, say I have a black & white vector style image above, and I want to run a video behind it in the white section and save it as an .avi (or any other common video file) how would I go about doing it? What software would I need? And if possible if someone can advise on the method or else point me in the direction of a comprehensive tutorial.

Many thanks in advance.

[poisondeathray]

Basically any video editor can do this. e.g. vegas, premiere, videostudio, edius , etc...

You put your image on top of the video, but you have to prepare the image first with an alpha channel (transparency) in the white area in an image editor (e.g. photoshop), so that the layer underneath (i.e the video) shows through the white area. The black can be left black if that's what you want it to appear as in the final video (it can be something else as well, doesn't have to be black.)

You can even put it together for free in avisynth, but it requires a bit of scripting knowledge.

[D138]

Awesome, thanks mate. Would you recommend any software in particular or are they all as straight forward as each other really?

[poisondeathray]

It's going to depend on your price range, what features you need, etc....

What you're asking to do is very straight forward. It's putting 1 layer on top of another. The hardest part is preparing the image with alpha channel, and that's pretty easy too...

I think you could do it completely for free with irfanview for the image, and wax for the video part

What is your input format (use mediainfo if you don't know) , and what is your output format goal (e.g. for dvd, web, pc use etc...)

[D138]

Yeah the alpha channel stuff is no problem, I'm quite into graphic design so that's ok, I just have no experience with video.

Input format would probably be .avi, and the output goal is projector via a laptop. It's for a projection for a friend of mine whos running an art installation. He has a digital image of a city scape, and I want to make the sky active and have it running as a video file, with the actual building structures/skyline just a solid image.

So I guess to make it relative to the "diagram" I posted the black sections will be solid images of buildings that don't change, and the white will be the active area where the video will be playing.

Hope that makes sense!

[poisondeathray]

Great, you're 1/2 done then. I would make a .png with alpha channel for the overlay. In video compositing, the layers are no different that what you would be doing in photoshop or other graphics programs. So you should be right at home.

The image should be the same dimensions of the video to make things easy. But you have to determine the aspect ratio of the video (if it uses square pixels or anamorphic) , otherwise you have to adjust the still image aspect ratio to match

BTW, .avi is just a container. It can hold different hundreds of kinds of audio & video streams. So saying "avi" doesn't provide very much information. I would use mediainfo to find out more characteristics and clues to the aspect ratio. For example a DV-AVI source wouldn't use square pixels

You also have to consider playback issues - what formats for software playback , what formats does the projector accept (like resolution) , type of laptop (i.e is it fast enough), AV connections for the laptop, etc...

[D138]

The aspect ratio of the projector is 1024 * 576 (16:9). What would be the ideal format for the video do you think?

Regarding playback, we were just going to burn the finished video onto a dvd and play straight from the laptop, with a vga cable running into the projector.

[poisondeathray]

Burn to dvd? Do you mean DVD-video or as a data disc for storage? Just playing the file from HDD would be better, more reliable and faster transfer rates. DVD-video is standard definition, so 1024x576 wouldn't work. It would have to be encoded to 720x576 with 16:9 AR (you're probably in PAL land?)

Something like xvid compression is low on CPU usage, and could be played back at 1024x576 25fps quite easily, even on older/slow laptops

Still need more information on the input video. e.g. fps, interlaced vs. progressive, input video dimensions . Because you may have to do other processing like resizing, deinterlacing etc... If you could use mediainfo (view=>text) and copy and paste the text information back here it would help

[D138]

Haha, PAL land indeed! Ok, I think I might have enough info here to take a chance on it. I'll report back and let you know how I got. Many thanks for all your advice, you've been a huge help. Cheers!

[D138]

Just saw the last part of your post. I'm actually unsure of the input video just yet as I havn't figured out where that's coming from yet.

[poisondeathray]

Well when you find out more information, you can post back. It's important to know the details, because something like interlacing would have to be deinterlaced for a progressive display (or deinterlaced on the fly during playback), and you may have to do other processing on the video like resizing to get the proper AR.

[D138]

Cool, ok man. I'll post back when I get those details. Thanks!