Converting RGBA to ARGB (glReadPixels -> AVAssetWriter)

Question

I want to record images, rendered with OpenGL, into a movie-file with the help of AVAssetWriter. The problem arises, that the only way to access pixels from an

Answer 1

Try calling

glPixelStorei(GL_PACK_ALIGNMENT,1) 

before glReadPixels.

From the docs:

GL_PACK_ALIGNMENT

Specifies the alignment requirements for the start of each pixel row in memory. The allowable values are 1 (byte-alignment), 2 (rows aligned to even-numbered bytes), 4 (word-alignment), and 8 (rows start on double-word boundaries).

The default value is 4 (see glGet). This often gets mentioned as a troublemaker in various "OpenGL pitfalls" type lists, although this is generally more to do with its row padding effects than buffer alignment.

As an alternative approach, what happens if you malloc 4 extra bytes, do the glReadPixels as 4-byte aligned starting at buffer+4, and then pass your AVAssetWriter buffer+3 (although I've no idea whether AVAssetWriter is more tolerant of alignment issues) ?