How can we make the saveFrame() method in ExtractMpegFramesTest more efficient?

Question

[edit] Reformatting into question and answer format following fadden@ suggestion.

In ExtractMpegFramesTest_egl14.java.txt, method saveFrame(), there is a loop for re

Answer 1

It turns out there's an even faster approach.

Using the suggestion in @elmiguelao's answer, I modified the fragment shader to do the pixel swap. This allowed me to remove the swap code from saveFrame(). Since I no longer needed a temporary copy of the pixels in memory, I eliminated the int[] buffer entirely, switching from this:

int[] colors = [... copy from mPixelBuf, swap ...]
Bitmap.createBitmap(colors, mWidth, mHeight, Bitmap.Config.ARGB_8888);

to this:

Bitmap bmp = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);
bmp.copyPixelsFromBuffer(mPixelBuf);

As soon as I did that, all of my colors were wrong.

It turns out that Bitmap#copyPixelsFromBuffer() wants the pixels in RGBA order, not ARGB order. The values coming out of glReadPixels() are already in the right format. So by doing it this way I avoid the swap, avoid an unnecessary copy, and don't need to tweak the fragment shader at all.

Answer 2

[edit] Reformatting into question and answer format following fadden@ suggestion

I wanted to suggest that this conversion can happen in the FragmentShader by changing the line

gl_FragColor = texture2D(sTexture, vTextureCoord);

into

gl_FragColor = texture2D(sTexture, vTextureCoord).argb;

which is an efficient shortcut to reorder in GPU the shader's output channels, that works in other ways too: .abgr or even .bggr etc.