Implement proper vcodec copy support via characteristics.

[fschaefer]

This is just a thought and basicly a crossposting from an issue posted at homebridge-camera-ffmpeg.

homebridge-camera-ui allows to set vcodec copy to speed up the stream without re-enconding. This fails if homekit requests a stream with resolution, bitrate, etc. that conflicts with just copying the stream, i.e. my yi outdoor cam works fine on my iPhone, but not on my iPad with vcodec copy.

Homekit supports video stream configuration via characteristics: HAP-Specification-Non-Commercial-Version.pdf - Video Attributes:

The Video attributes allow the accessory to indicate supported resolutions, frame rates etc., This information is encoded as a tlv8- the list of types for the value of this TLV are as follows [...]

Can we force Homekit to request the streams in their native resolution via characteristics, so we can use vcodec copy?