openh264dec: Don't forget to unref the input state
openh264dec: Optimize frame copying a bit
openh264dec: Add support for GstVideoMeta

This will make operation with various sinks faster for free.
openh264enc: Add support for GstVideoMeta

This will allow upstream elements to work more efficiently.
openh264enc: Fix up caps and stride handling
openh264enc: Switch to an adapter for the output

Appending too many memories to a buffer is going to be slower
as it will cause copy of the buffer and then appending of the memory.
openh264enc: Properly drain the encoder on ::finish()
openh264dec: Properly drain codec on ::finish()
openh264dec: As we require NAL alignment from upstream we don't need to parse anything
openh264dec: GstVideoDecoder works on frames, not sub-frames (e.g. NALs)

And we can just pass complete AUs to the decoder without problems.
openh264dec: Don't drop videocodec frames if we can't decode them *yet*

Fixes jittery playback of streams with B frames.