Capture audio in a seperate thread. It ensures that --input-slave oss:// runs independent of the video capturing and resulting in higher throughput.

This is a workaround for the Neuros OSD 2 linux kernel 2.6.23. Since vlc does a poll before a read it is guaranteed that there is data, thus using O_NONBLOCK does not really add any advantage here.

This reverts commit 3e1c59ce.

This reverts commit f86d0e82.

Fixes:
- compiler warnings on unused variables
- comparing correct types
- optimized calculations

The framerate calculation previously done in v4l2 access input was always late. Reworked the calculation to move closer to the requested framerate by setting a new frame grab deadline based on grab-date + duration + late (deadline miss). On a fast CPU it will not make much difference, but on a slow CPU the algorithm will grab frames based on FPS settings.

cleanup commit-id: dfa08f13