And comments

__GCC_HAVE_SYNC_COMPARE_AND_SWAP_ is neither defined nor is an equivalent macro available. However, the protected features are supported.

This leaves only synchronization code in input.c. This patch introduces
a small regression where resampling adjustment have a latency of two
packets instead of currently one. That will be fixed later.

The number of channels is conveyed in the channels mask.

Close #7739

The button state now indicates if the next video will be started in
fullscreen, or there is already one video in fullscreen.

This removes unused pointering. Furthermore, for nonembedded windows
the video size is set directly to avoid strange resizing after window
creation.

This was not a particularly good idea in user space.

The code is complete and utter crap either way.

(Single precision is more than enough in this case.)