OpenGL pixel transfer inside GPU - opengl

Question

I have been working with VR recently and encountered some OpenGL related problem.
The API i use for VR capture a video stream and write it to a texture, I, then, want to submit this texture to a headset. But there is an incompatibility in the API : the texture I get from the stream has an undefined internal format and cannot be submitted to the headset directly.
I am working on a workaround, for now, I have used a GPU -> CPU -> GPU transfer :
I read the first texture pixel (with glReadPixels) and write them into a buffer, then I use this buffer to create a texture with the correct format. This works fine but has some latencies due to data transfers.
I have been trying to do a direct GPU copy but failed :
I tried using PBO but have problems with invalid operation (following http://www.songho.ca/opengl/gl_pbo.html), here is the code with a invalid operation on glReadPixels
// Initialization
glGenBuffers(1, &pbo);
glGenTextures(1, &dstTexture);
glBindTexture(GL_TEXTURE_2D, dstTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
// Copy to GPU
glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
glBufferData(GL_PIXEL_PACK_BUFFER, bufferSize, NULL, GL_DYNAMIC_DRAW);
glBindTexture(GL_TEXTURE_2D, id); // texture given by the API
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
glBufferData(GL_PIXEL_UNPACK_BUFFER, bufferSize, NULL, GL_DYNAMIC_READ);
glBindTexture(GL_TEXTURE_2D, dstTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
I tried using FBO but encountered pointer exceptions.
glCopyImageSubData does not work because the first texture internal format is not recognised.
What are the steps to do a direct GPU copy?