I would like to have an alpha mask over a video recording, and when you finish recording, then the final video has this mask over. Do you know what I mean?

But I have being looking for it and I have not found nothing.

Please could you help me?

I leave you my email.

thaks a lot!

Thanks,

James

The rolling ball loop has been rendered as movie plus mask by our artists and we converted it to 192 transparent pngs offline. We then created 3 atlases of 64 frames each loaded as textures of the size 1024×1024. Using thumbnailimageAtTime was just an idea you might follow to do this online – directly in your app.

To apply masks with OpenGL ES 1.1 (this applies to cocos2D) you can use FBOs to change the alpha channel in a second step after you had rendered to them. Cocos2d supports this with CCRenderTexture directly.

Cheers,
Heiko

Thanks very much for your reply. You summarised what I would like to do exactly.

So if I understand correctly, to achieve your affect of having the water flow in front of the sphere, you took random frames of the playing movie (using thumbnailImageAtTime:timeOption) which returned a UIImage; which you then convert to a mask and put in a UIView. You then convert the UIView to a EAGLView? This is a very useful tip!

We are using Cocos2D because we also have sprites to draw in another layer. Do you add the mask layer as a node to the sprite layer? How do you blend the two layers to mask the sprites? I am sorry for the rudimentary questions – I am new to OpenGL programming.

Thank you again for your invaluable help.

Best regards,
Ash

I am glad I could inspire you with my blog post about video composition. In general, you can place any UIView on top of the rendering view of a MPMoviePlayerController as you can read on different online tutorials. If your particular UIView contains transparent areas the content of the movie shines through.

What you want to achieve is the opposite, though. Parts of your movie should be rendered transparently based on its content (chroma keying). I share your opinion that this is currently not possible. Neither can you place a UIView behind the movie (until SDK 3.2) nor can do you have live access to the frames. What you could do though, is storing the individual frames as sprites if this fits in memory (you can render thumbnails of random frames to UIImages, since 3.2).

Hope this helps.

Cheers,
Heiko

Thank you very much!