webcam rc stuttering

[jnvsor]

Upstream issue: https://trac.ffmpeg.org/ticket/3192

[jnvsor]

Workaround committed in 6bf7114 (v2.0)

To be reverted when ffmpeg bug 3192 is fixed

[jnvsor]

Due to new mapping system the stutter bug is now present in the webcam rc, workaround has been moved there.