Encoding

This subsystem synchronizes the client and the server's encodings so that each end can use the most appropriate codecs for exchanging data.

Component	Link
client	xpra.client.subsystem.encoding
client connection	xpra.server.source.encoding
server	xpra.server.subsystem.encoding

The client advertises an encoding dictionary. The interoperability fields are:

Capability	Purpose
options	Encodings the client can accept
core	Concrete decoder encodings, without aliases
window-icon	Encodings accepted for window icons
setting	Requested default encoding
rgb_formats	Raw RGB pixel formats the backing can paint
full_csc_modes	Codec-to-colourspace conversion modes
quality, min-quality	Requested quality bounds
speed, min-speed	Requested speed bounds
video_max_size	Maximum video dimensions
batch	Damage batching parameters

Codec profile maps such as h264 extend these fields. Unknown codec diagnostic and version fields are advisory.

Any video codec map may also carry a level (ie: h264 → level = 4.1), which caps the resolution, framerate and bitrate the server's encoder may use, so that a client with a constrained decoder can ask for a stream it can keep up with. A <colourspace>.level key applies to that colourspace only. The level is written the same way for every codec, and the server converts it to whatever its encoder expects. It is a request: a server whose encoder cannot honour it logs a warning and encodes at the level it would have chosen anyway. Without this capability, no level is imposed and every encoder signals the lowest level the stream it is producing actually requires.

Packet Type	Direction	Arguments	Purpose
encoding-set	client to server	encoding name, optional window IDs	Select an encoding
encoding-set	server to client	properties dictionary	Publish updated encoding and video specifications
encoding-options	client to server	options dictionary	Update quality, speed, scaling or batching
encoding-config	client to server	encoding capability dictionary	Replace the client's decoder configuration