Init audio encoders only once

Move the initialization functions so they only happen once when the
file is opened.

This seems to be working, which must mean that the decoders are never
called on separate threads simultaneously. This seems to be working,
although I did get a crash at one point.I haven't been able to
reproduce, but I'll be careful and leave this on a branch for a while
until I'm really confident it's working.
Initialize video decoder once also
ReadMe typo
Changes to make WebP work in After Effects
Add 48 fps option

Includes 47.952 fps
Move vd and vb out of the global state

They should be initialized every time we decode.

Our earlier crash was caused by these being cleared when they had never
actually been initialized.
Delete DS_Store