Say you have a 20 second video (perhaps taken with the device camera) and you want to add an overlay in to the video.
(The overlay would simply be a normal raster image, i.e. an Android Image (doc).)
You want to create a new video, with the overlay as part of the video image, and save the video.
In fact, can MediaCodec SDK be used to do this job?
https://developer.android.com/reference/android/media/MediaCodec
In the past, you would usually use FFMPEG for such a problem, but that is a mess and slow.
Is MediaCodec possible here?
Since it is "new" I just can't find any information on this.....
this is possible using MediaCodec. For a start, take a look at the DecodeEditEncode example from here
This example is shows how to resize a vide using a OpenGL ES shader. What you want to do is render your overlay over the video also using a OpenGL ES shader.
Another good source for examples on MediaCodec can be found here
Here you can find some examples on how to use basic rendering techniques. Look at the Hardware scaler exerciser.
When you have the video part up and running, this is probably where the actual struggle starts since there are no standard methods to render text in OpenGl ES. I'd probably just draw text to a Canvas and make a texture out of it, probably is slow though.
If you have a static overlay, like a watermark, you could create it beforehand and ship as a resource.