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 |