synapse-runtime-sdk

The Python SDK for the Synapse runtime: publish and subscribe to topics, serve and call services, keep shared values current with the store, and move H.264 video — all from asyncio.

pip install synapse-runtime-sdk              # the SDK
pip install "synapse-runtime-sdk[video]"     # + the H.264 encoder/decoder (CPU or NVIDIA)

Linux x86_64, Python ≥ 3.11. A Synapse runtime to connect to: curl -fsSL <release host>/install.sh | bash.

The surface in one screen

from pydantic import BaseModel
from synapse_sdk import Synapse, Topic, Service, Api, ServiceError, SynapseError

class Imu(BaseModel):
    accel: tuple[float, float, float]

imu = Topic("imu", schema=Imu)                                   # datagram (default): one datagram per message, newest wins
log = Topic("log", delivery="stream")                             # ordered, nothing dropped
api = Api(arm=dict(get_pose=Service(input=dict, output=dict)))    # api.arm.get_pose.name == "arm/get_pose"

node = Synapse("agent", "sim-1")                              # type agent|observer|web|hmi; the name is minted when absent; idle
await node.connect("https://localhost:4470")                  # bounded first connect; the newest connect() wins
pub = await node.publisher(imu)                               # resolves once the runtime admitted it on the current session
pub.publish(Imu(accel=(0, 0, 9.8)))                           # synchronous; validated by the schema; dropped+counted while unbound
async for batch in node.subscribe(imu):                       # one read = the newest message of each publisher (queue_depth=0: every message)
    for msg in batch:
        print(msg.publisher, msg.data.accel, msg.t_us)
sub = node.subscribe(imu, on_imu)                             # the callback form: the SDK runs that loop, on_imu(batch) (def or async def)
view = node.view(imu, stale_time_ms=200); await view.ready(); print(view.get().data)   # the value now; changed() / watch() / on_change(cb)
reg = await node.serve(api.arm.get_pose, lambda inp, ctx: {"frame": inp["frame"]})   # (input, ctx) -> result; sync runs in a thread, async on the loop
pose = await node.call(api.arm.get_pose, {"frame": "tool0"}, deadline_ms=1000)       # await the Run for the result
run = node.call("arm/move_to", {"target": 1}); async for u in run: ...; await run   # updates are a stream (run.next(): None at the end); await run.cancel()
run = node.call("arm/move_to", {"target": 1}, on_update=self.on_progress)                # the callback form; the end: run.add_done_callback(cb) → cb(run), run.result()
board = await node.store("mission/board", access="public"); await board.set(phase="loading", step=4); board["phase"]   # a value kept current, read like a dict
@node.every(hz=50)                                            # a fixed grid while the node lives (polling bridges)
def poll(): pub.publish(read_imu())
await node.close()

• Identity: Synapse(type="agent", name=None, *, user_id=None, credential=None, ...): who the node is, never where it connects. type bounds the role the runtime grants on the ladder observer < agent < operator < hmi < admin (agent → agent; hmi → hmi from admission, never promoted or demoted; web → observer until promoted to operator on a project); a web/hmi node without user_id mints one. The node is usable at once and idle until connect(). node.info() has name, prefix, role, robot, runtime_id, broker_version.
• Connecting: await node.connect(url), the one connect verb: the first connect, and how an HMI moves from one robot's runtime to another (the current session is torn down first; every handle re-binds to the new one). url is the runtime, https://host:4470. Through a relay, give the relay with the runtime's path, https://relay:4443/runtimes/<runtime_id> (runtime_id from node.info() of a node connected directly, or the runtime's banner), and token= the relay token (a jwt= in the URL is taken as the token; neither is ever printed). type=, name=, user_id=, credential= given to connect() change the identity there; left out, the node's are kept. Operator intent is never lost under quick clicking: the newest call wins (a superseded connect() returns quietly); the target already declared is a no-op. With no url, connect() settles with the target already declared, else connects to $SYNAPSE_ENDPOINT (set by the runtime for every task it starts), else raises invalid_input. await node.disconnect() leaves the target: the node rests idle with every handle kept, until the next connect(). A name a live node already holds is refused admission_refused (retryable); no answer within connect_timeout_ms is not_connected (through a relay: check the token); a relay address without the runtime's path is invalid_input. The first connect tries a retryable failure again for up to 30 s (a hard bound), then raises it; the node rests failed, still usable. For cleanup on every exit path, async with await Synapse(...).connect(url) as node: (or async with Synapse(...) as node: in a task, which connects to $SYNAPSE_ENDPOINT).
• Sessions come and go, the node stays: a lost session is replaced (reconnect=True, backoff reconnect_initial_ms → reconnect_max_ms), every publisher, registration, subscription and namespace replays its intent on the new session; in-flight calls fail connection_lost; nothing is resumed. node.status is a state value, read like every handle: node.status.get(), async for s in node.status.watch(), await node.status.changed(), node.status.on_change(cb) (so are node.catalog and node.project). reconnect=False rests the node failed on a drop (not ended: connect() dials again).
• The runtime decides: publisher(), serve(), store(), scene() resolve on admission (made before the first session, or between two, they resolve on the next one); a refusal (already_registered, unauthorized, owner_taken, ...) is asked again, paced, with a warning each time (warn= callback, default logging).
• Time: t_us is the publisher's clock, microseconds. node.now_us(), node.age_us(msg) (how old a message is in our clock, with its error bound, or None when the clocks are not comparable); deadline_ms= on a subscription drops a message older than that in our own time domain.
• Errors: one SynapseError(code, message, data, retryable); ServiceError(code, message, data) raised by a handler crosses verbatim (data.app for an application code); the same error codes in every language.
• Video: cam = await node.video_publisher("gs/video") then cam.publish(image); async for image in node.video_subscriber("gs/video"); see below. A video topic is Topic(name, content_type="video/h264"): datagrams with loss repair unless fec= says otherwise; pub.publish(access_unit) on it sends one H.264 access unit, and a subscriber that names the topic gets bytes with msg.key / msg.config / msg.recovery.
• Bodies follow the topic: a subscription decodes what the runtime says the topic carries — msgpack topics give values (validated by your schema when the Topic has one), any other content type gives bytes.
• The certificate pin (connect(url, broker_cert_sha256=...)) is discovered when absent (SYNAPSE_BROKER_CERT_SHA256, then http://host:port/certificate.sha256). SIGINT/SIGTERM close every open node, then re-raise (signals=False opts out).
• Timeouts and periods are _ms integers everywhere, in every language.

Store

A namespace is a value the runtime keeps current: {key: value}, shared by every node of the active project. The handle reads like a dict that changes under you, as os.environ does: each read is the value now. Writes go to the runtime and are awaited, so they are verbs, never assignments (board["phase"] = "x" raises TypeError naming the verb).

board = await node.store("mission/board", access="public")   # resolves once the value is current
board["phase"]; "phase" in board; len(board); board.items()  # the value now; board["nope"] raises KeyError
board.get("phase", "idle")                     # that key, or the default
snapshot = board.get()                         # the snapshot: the whole value in one read, a plain dict that stays as it was
await board.set(phase="loading", step=4)      # one atomic write; also set({"with space": 1}) and set("phase", "x")
await board.delete("step"); await board.clear()   # each resolves once a read shows it
async for value in board.watch(): ...          # the whole value after each change; watch("phase") for one key
value = await board.changed()                  # the whole value after its next change
off = board.on_change(lambda value: ...)       # the callback form: cb(value) after each change; off() removes it
board.synced                                   # current or not
board.status.get()                             # why: the handle's own state, a state value (connected, pending, mode, owner, ended, ...);
async for st in board.status.watch(): ...      # ... after each change; await board.status.changed() for the next

The runtime decides every write: not_owner, unauthorized, store_gone raise from the awaited verb. dict(board) also copies, but key by key: while someone writes, it can mix two versions; board.get() keeps keys written together together.

Scene

The active project's world: one set of entities (frames, robots, objects, cameras …) the runtime keeps for the project. Writes go through two namespaces. scene.authored writes what exists — the hierarchy and the components — and every write is one atomic batch the runtime checks. scene.live writes what is happening now — poses, joint positions and state of entities, and live entities of this node's own — many times a second, never saved. What you read is both merged: a live pose replaces xform.t/xform.q of the entity it names; removing it brings the authored value back. Names are global: one name, one entity, whichever namespace wrote it.

from synapse_sdk import Kind                   # Kind.FRAME / ROBOT / MODEL / SCAN; every kind parameter also takes any string

scene = await node.scene()                     # the active project's scene; detached (empty) while no project is active
await asyncio.wait_for(scene.ready(), 10)     # until a project's scene is in: current as of the attach (at the version the runtime answered)
world = scene.get()                            # {id: entity}, read once to build a simulation from it
scene.tree(); scene.query(lambda e: e["kind"] == "robot")   # the value now; tree() = [{id, children}]

# a builder's one verb, keyed by name; the id is the runtime's answer: the spawn is sent, and when the name is held the
# runtime's name_taken names the holder, which is patched only where it differs (nothing more sent when equal; live
# overrides never count); parent is for the spawn only; a holder of another kind: name_taken as it came
tool = await scene.authored.upsert(Kind.FRAME, name="tool", parent=None, xform={"t": [0, 0, 1], "q": [0, 0, 0, 1]})
tool.id                                        # the entity's view comes back (by id); every entity argument takes an id or a view

# one entity as a view: what upsert returns, or by id or by name (a view by name follows the name to whichever entity holds it)
tool = scene.entity(name="tool")               # or scene.entity(id): merged, authored with its live overrides
tool["xform"]; "xform" in tool; len(tool)      # read like a dict over its components, now
tool.get("xform", None); tool.get()            # a component or the default; get(): the entity in one read (a copy), None when absent
tool.authored.get(); tool.live.get()           # one plane: the entity as declared; its live row ({entity, pose, joints, state, stamp})
await tool.authored.set(props={"speed": 2})    # one patch of the authored entity (also set({...}), set("props", {...}))
tool.live.set(xform={"t": [0, 0, 1.1], "q": [0, 0, 0, 1]}, joints={"j1": 0.3}, state={"badge": "on"}, lifetime_ms=500)   # its live lanes, synchronous
await tool.live.remove()                       # the release call: its live row gone, back to authored
async for xform in tool.watch("xform"): ...    # that component each time it changes (latest wins); watch() for the whole entity
landed = tool.changed()                        # the entity after its next change, armed at the call (arm it before the write)
scene.status.get()                             # a state value: state (attached | detached | closed), synced, pending, version, hash,
                                               # detached_drops, unclaimed_drops; status.watch() / status.changed(); scene.synced

# authored: each resolves once scene.get() shows it; a refusal (locked, name_taken, invalid_tree, ...) raises
id = await scene.authored.spawn("box", parent=None, name="crate", xform={"t": [1, 0, 0]}, visual=[{"kind": "box", "size": [1, 1, 1]}])
await scene.authored.patch(id, props={"mass": 2}); await scene.authored.rename(id, "crate-1")
await scene.authored.reparent(id, other, before=sibling)
await scene.authored.set_locked(id, True); await scene.authored.despawn(id, cascade=True)   # cascade: with its subtree
async with scene.authored.txn() as t:          # one atomic batch when the block ends
    a = t.spawn("frame", name="a"); t.patch(a, props={"k": 1})

# live: decisions are calls, data is streams
cup = await scene.live.upsert("detection", name="cup", parent=tool, lifetime_ms=500, props={"score": 0.93})   # the claim call: the view of the runtime's id
await scene.live.remove(cup)                   # the release call: an override back to authored; a live entity gone
scene.live.batch(poses=[{"id": arm, "t": [0, 0, 1], "q": [0, 0, 0, 1]}], joints=[{"id": arm, "j": {"shoulder": 0.3}}], lifetime_ms=500)   # a sim's tick: lanes only, synchronous
scene.live.batch(state=[{"id": arm, "s": {"badge": "serving"}}])

async for world in scene.watch(): ...          # the entities after each change (await scene.changed() for the next; scene.on_change(cb))
                                               # engine feeds: watch_live_removals(), watch_live_denied()

• An entity view reads like a dict that changes under you (as the store handle does); an entity that is not there (no entity holds the name, the id is gone, the scene is detached) reads as an empty mapping, never an error. Writes are verbs: tool["xform"] = x raises TypeError naming await tool.authored.set(...). The view's two planes, tool.authored (get, set) and tool.live (get, set, remove), are one object each for the view's life and have no watch/on_change/changed of their own: the view's cover the entity, whichever plane changed.
• view.live.set(...) writes three lanes: xform ({"t", "q"}, both, nothing else), joints, state; anything else is invalid_input. The first lane write for an id this node has not claimed asks the claim (upsert {id}, a call) and the latest row per lane is held until the runtime answers, then sent: a single write lands. A refusal drops the held rows (counted in status.get().unclaimed_drops), is a node notice (node.notices()) and is asked again, paced, by a later write. await scene.live.upsert(...) is the claim call (name optional): it returns the view of the id the runtime answered (a name this node already claimed keeps its id; a taken name raises name_taken {name, id, holder}, another session's id not_owner, nothing kept). A granted claim is claimed again, same id, on every reconnect and project switch (a refusal asked again, paced, with a warning) until await scene.live.remove(x) or await view.live.remove(); closing the node's last scene handle releases them all. The id is never a component: id= on either upsert is invalid_input.
• Keyword names: name and parent (and lifetime_ms on scene.live.upsert) are parameters of upsert, so a component of that name cannot be given there by keyword; await view.authored.set({...}) and patch(e, {...}) take any component name.
• Two kinds of users. A node author (a driver, a sim, a task) needs node.store() with get/set/watch, scene.authored.upsert() keyed by name (its view back), scene.entity(id) / scene.entity(name=...) with get/watch/authored.set/live.set, scene.live.upsert() for a live entity of its own and scene.live.batch() for a sim's one write per tick. An engine or editor builder adds scene.authored.spawn/patch/rename/reparent/ despawn/set_locked, txn/apply, one plane alone (view.authored.get(), view.live.get()) and the engine feeds (watch_live_removals, watch_live_denied). Every handle (store, scene) has one shape: get(), ready(), status (a state value: get(), async for … in watch(), changed(), on_change(cb)), synced, watch(), changed(), on_change(cb), close().
• A live row with lifetime_ms goes away that long after its last write (timeout on watch_live_removals()), and when its writer leaves; one without it stays (a parked robot). The session that claimed an id holds it; another session's claim of it is refused not_owner (a node notice, and its ids on watch_live_denied()). A name another entity holds is refused name_taken, its data["holder"] the holder's id.
• While detached, authored verbs raise project_inactive and lane writes are dropped (counted in status.get().detached_drops). A closed handle reads nothing (get() is {}, views are empty, tree() is []) and its verbs raise not_connected.
• Helpers: ulid() (a fresh entity id), order_between/order_before/order_after (sibling order values), derived_frame_name(parent, frame).

Derived frames

A robot's robot.frames (names of links) and an entity's hardpoints (named mounting points with a pose) each stand for frame children of that entity, marked flags.derived. materialize_frames and materialize_hardpoints keep those children in step with the declaration: they spawn what is missing, rename the frames after the entity is renamed, set a changed pose, and remove a frame that is no longer declared (refused, as a veto, when something is parented under it). They only add ops to a txn and return a report of what they did; nothing is sent until the block ends.

from synapse_sdk import materialize_frames, materialize_hardpoints

async with scene.authored.txn() as t:          # when a scene is loaded: no poses, so nothing is spawned or moved
    report = materialize_frames(t, robot, scene.get())
async with scene.authored.txn() as t:          # after an edit of the robot: the rest poses are your FK at its joints
    report = materialize_frames(t, robot, scene.get(), {"tool0": {"t": [0, 0, 1.2], "q": [0, 0, 0, 1]}})
    if not report.clean:                       # raising here sends nothing
        raise RuntimeError("; ".join(report.errors + report.vetoes))
async with scene.authored.txn() as t:          # hardpoint frames take their pose from the hardpoint itself
    materialize_hardpoints(t, entity, scene.get())

The report: frames (each declared name → its frame's id), spawned, updated, removed, vetoes, errors, and clean (no vetoes, no errors). A declared frame that does not exist yet and has no pose given is an error, never a spawn.

Tasks

A task is a program the runtime starts and keeps running for you (a driver, a simulator, a planner). You declare which tasks to run; an operator runs and stops them. There are two kinds, and stopping one kind never touches the other:

• Robot tasks belong to the robot and keep running when the active project changes (an arm driver). The runtime keeps their declarations across restarts.
• Project tasks belong to the active project: the tasks component of its scene's entities (one component; it replaces the prototype's behaviors). Switching projects stops them.

A declaration is {ref, enabled?, config?, schema?} under an instance name: ref is the task's address (as the task tool lists it), enabled: False leaves it out of the next run, config is passed to the task, and schema pins the task's schema hash (a different one fails the run). Whether a task has a process to run is the task's own spec: one with nothing to run is passive, counted and never started (something else uses its config, a simulator say).

Everything is under node.tasks, the same object for the node's life:

t = node.tasks

# robot tasks (operator role)
cam = await t.declarations.set({"ref": "python:camera:driver", "config": {"fps": 30}})   # the SDK mints the instance; returned
await t.declarations.set("arm", {"ref": "python:ur-driver:driver", "config": {"host": "10.0.0.5"}})   # or a stable key of yours
await t.declarations.set("arm", {**t.declarations["arm"], "enabled": False})         # off for the next run

# project tasks: the `tasks` component of a scene entity
scene = await node.scene()
await scene.authored.patch(sim_id, tasks={"sim": {"ref": "python:mujoco-sim:sim"}})

r = await t.run_project_tasks()        # {"launched": 2, "passive": 3}
await t.stop_project_tasks()           # None, also when nothing ran
await t.run_robot_tasks()
await t.stop_robot_tasks()

await t.status.ready()                                          # the value is in
t.status["project"]["state"]                                    # "starting" | "running" | "stopping" | "stopped" | None (not said yet)
t.status["project"]["tasks"].get(entity_id, {}).get("sim")      # {"scope", "addr", "instance", "entity", "state": "up" | "down", "since", "restarts", "exit"?, "log"}
t.status.get()                                                  # the whole status: {"robot": ..., "project": ...}
t.catalog["python:ur-driver:driver"]                            # {"addr", "workspace", "pkg"?, "name"?, "inputs"?, "schemaHash"?, ...}

async for s in t.status.watch():                                # the whole status after each change
    arm = s["robot"]["tasks"].get("arm")
    if arm and arm["state"] == "down":
        print(f"arm exited {arm.get('exit')}, {arm['restarts']} restarts; log {arm['log']}")

• Each of declarations, status and catalog reads like a dict, as a store handle does (t.status["robot"], "arm" in t.declarations), beside get() (the whole value in one read). declarations writes with awaited verbs (set, delete, clear; also synced, status, watch, on_change, ready); a write waits for the value to be current, then resolves once a read shows it; set(declaration) mints the instance (a ulid) and returns it, set(instance, declaration) writes the one named, set({instance: declaration, ...}) several at once (one mapping is a declaration when its ref is a string; the same program may be declared many times). status and catalog are read-only: the runtime writes them (synced, ready(), watch(), on_change(cb); item assignment raises TypeError). Each opens the first time you touch it; the verbs open nothing.
• status.get() is {"robot": {"state", "since"?, "reason"?, "tasks": {instance: task}}, "project": {..., "tasks": {entity_id: {instance: task}}}}. reason says why a run stopped or failed (project_switch, or an error code). exit is {"code", "at"}, {"signal", "at"} or {"at"} (Unix ms). A part that did not change keeps its object (is tells what changed). watch() is state, not history: a slow reader sees the latest status, and restarts is the count to trust.
• A run checks every enabled declaration first and starts nothing unless all pass. A failed check raises preflight_failed, a task that could not be started launch_failed (what had started is stopped); both carry e.data["report"], one entry per declaration at fault: {scope, entity?, entity_name?, instance, addr, reason, detail?} with reason one of missing (unknown address), schema_mismatch, spec_error, invalid_input (the config); is_tasks_refusal(e) tells them apart. A second run while one is running raises already_running; a project run with no active project project_inactive. A run's reply is the runtime's answer; what runs afterwards is status.
• A task that exits is started again after a delay that grows (by default from 1 s up to 10 s) while it keeps exiting. A crash loop never ends the run; restarts climbs.
• Running and stopping need the operator role or above: an hmi node, or a web node promoted on the active project. Robot tasks need only that role; project tasks also need an active project (project_inactive otherwise).

Writing a task

A task owes the runtime nothing. A task is any program the task tool can describe. The runtime asks the tool for the task's spec at every run and starts the spec's command directly; your declaration's config reaches it as the spec's flags, positionals or environment variables. The program never has to connect, report or handshake. What the runtime does to it:

• Environment: cleared, then exactly the spec's env, then the stamps below. There is no PATH or HOME unless the spec sets them. Working directory: the spec's cwd. No stdin.
• Output: stdout and stderr are appended to a log file, with one header line per start; its path is log in the status. Python buffers stdout when it is a file: set PYTHONUNBUFFERED=1 in the spec's env, or print(..., flush=True).
• Stop: SIGTERM to the program's process group, then SIGKILL 5 s later. Handle SIGTERM and leave within 5 s.
• Exit: any exit is followed by a new start after a delay (1 s doubling to 10 s, back to 1 s once a run lasted longer than 10 s); restarts and exit in the status show it.
• Runtime gone: the program gets SIGTERM.

The stamps (optional to read):

A plain task (no SDK at all):

# serve.py; its spec: argv ["python3", "serve.py"], mapping port → {as: "flag", flag: "--port"}
import argparse, http.server, signal, sys
p = argparse.ArgumentParser(); p.add_argument("--port", type=int, default=8080); a = p.parse_args()
srv = http.server.ThreadingHTTPServer(("0.0.0.0", a.port), http.server.SimpleHTTPRequestHandler)
signal.signal(signal.SIGTERM, lambda *_: sys.exit(0))          # the runtime stops us with SIGTERM
srv.serve_forever()

A task that talks to the runtime (a simulator's shape):

import asyncio, json, os, signal
from synapse_sdk import Synapse, Topic
from synapse_sim.util import JointStates                         # the simulator's own message model

config = json.loads(os.environ.get("SYNAPSE_CONFIG", "{}"))     # or flags from the spec's mapping

async def main():
    stop = asyncio.Event()
    for s in (signal.SIGINT, signal.SIGTERM):                    # our own graceful path; the SDK leaves an installed handler alone
        asyncio.get_running_loop().add_signal_handler(s, stop.set)
    node = Synapse(type="agent", name="sim-server-1")
    await node.connect()                                                     # no url: $SYNAPSE_ENDPOINT
    state = await node.store("mujoco/state", access="protected")             # ours alone; a second sim waits
    scene = await node.scene(); await asyncio.wait_for(scene.ready(), 10)
    joints = await node.publisher(Topic("ur5e/joint_states", schema=JointStates))   # once; publish() is sync
    async def control(req, ctx):                                             # (input, ctx); ctx.update() is sync
        ...; return {"result": "stopped"}
    await node.serve("mujoco/control", control)
    await state.set({"simulation_status": "stopped", "sim_time": 0.0})       # one atomic write, resolves when visible
    # loop: joints.publish(...); scene.live.batch(joints=[...], poses=[...], lifetime_ms=2000)
    await stop.wait()
    await node.close()

asyncio.run(main())

A name is not taken from SYNAPSE_INSTANCE for you: two entities with an instance sim would collide. Give each task's node its own name (from its config, say).

Examples

Getting started, one verb per file: examples/getting-started/python/01_connect.py … 14_live.py in the repository.

Video

Needs the extra: pip install "synapse-runtime-sdk[video]" (without it the two calls below raise MediaError saying so).

cam = await node.video_publisher("gs/video")       # resolves once the topic is admitted
cam.publish(image)                                  # numpy uint8 (h, w, 3) RGB: convert + encode + publish in one call
cam.publish(image, t_us=capture_us)                 # the capture time, if you have one (default: now)
cam.close()

async for image in node.video_subscriber("gs/video"):   # decoded pictures
    print(image.width, image.height, image.t_us)
    frame = image_to_numpy(image)                       # (h*3/2, w) I420; np.asarray(image.y) is the luma plane, no copy
node.video_subscriber("gs/video", on_image=show)       # or a callback per picture (def or async def)

• publish is synchronous and queues nothing: the caller waits for one conversion + encode (about a millisecond at 640x360). The picture's format comes from its shape — (h, w, 3) RGB, (h, w, 4) RGBA, (h*3/2, w) I420, a tuple of planes (y, u, v) (I420) or (y, uv) (NV12); pixel_format="bgr24" for OpenCV pictures.
• Options of video_publisher, all optional: pixel_format, fps (nominal, for rate control; 30), bitrate_kbps (2000), backend ("auto": NVIDIA when present, else CPU).
• One publisher, one size: the encoder is made from the first picture; a picture of another size raises SynapseError("invalid_input").
• A subscriber that joins mid-stream starts at the next picture it can decode, and asks the publisher for one when it waits too long; close() stops it.
• The encoder and decoder are also there on their own (H264Encoder, H264Decoder, TestPattern in synapse_sdk.media) for a pipeline of your own.