(cherry picked from commit ba9d2cd7)

(cherry picked from commit 7010d0c5)

(cherry picked from commit 0e96e789)

(cherry picked from commit 164d7af8)

(cherry picked from commit 7cab9fcb)

(cherry picked from commit e1cd5ee5)

- Setting a valid max_rate (via vb=) seems to cause random crashes.
- Don't set any max_rate from ffmepg if vb is 0.

include 03e013a6b77ddf7fa0fe99af77803d3e6071ff6d

(cherry picked from commit a0f2f3ad)

(cherry picked from commit 4093638c)

(cherry picked from commit dbd8424f)

(cherry picked from commit c7bcb7be)

(cherry picked from commit d3f70246)

(cherry picked from commit 970cc7ee)

Signed-off-by: Felix Paul Kühne <felix@feepk.net>
(cherry picked from commit a3622aa4)

build script, xcodeproj and podspec: raise minimal versions for iOS and tvOS to support VideoToolbox in FFmpeg

On iOS, we require 8.0, on tvOS 10.2

This is needed for chromecast, to encode when there is no VT encoders.

This is needed for chromecast.