Watch it keep working while everything changes.

The largest one

Per-client rate adaptation

What should happen. A transmitter sends at the best rate it can manage and does not care how fast anyone receives it. Each client gets its own non-blocking socket, the relay streams to all of them in parallel, and the resolution adapts per leg. A slow participant sees a smaller picture. Nobody else notices they are there.

What actually happens. The relay is a byte fan. It can pass a frame to a viewer or drop it, and that is the entire set of moves available to it — it never decodes anything, which is exactly why it is small and fast and content-blind. So the only way it can serve a constrained client is to drop whole frames, and dropping every third frame of a 1280×720 stream does not produce a smaller picture. It produces a slideshow at full resolution: a low frame rate, no pixellation, and a viewer wondering whether the call has frozen.

What happens instead. Each receiver publishes what it is getting and whether it is keeping up, and every participant derives the call's rate from those rows. The consequence is unchanged — the call still runs at the slowest participant's rate — but it is no longer a misdirected report. It is one stream and one rate by design, bounded by the slowest published report, with the slow end identified by name. That is an architecture, not a bug.

Even fixed, that only shares the pain more fairly. The transmitter would still be sending one stream and the slowest participant would still decide what it is. What it needs is transcoding at the relay — decode once, encode per client at that client's budget, with the ladder applied per leg rather than per call. The per-leg budget already exists and is already enforced; what is missing is the ability to send a client something other than what arrived. That is the difference between a relay that forwards and a relay that serves.

Still open, unchanged

Receive-side audio priority

On the way out, audio takes precedence over video for the shared wire — a voice packet never waits behind a keyframe. On the way in, frames are handled in arrival order. The same rule should apply in both directions and currently does not.

New · found since

The store returns partial results under load

Ask it for everything and, under enough load, it answers with less than everything. The rate loop is deliberately tolerant of that; nothing else is.

New · found since

Capture hardware lies about its limits

One USB camera delivers 1.5 of a wanted 50 samples a second; one platform's camera backend ignores a request for single-frame buffering and queues frames — which arrives downstream looking exactly like a link that stalls and recovers. Both are detected and named rather than mistaken for network trouble. Neither is fixed.

New · found since

Software encode is the ceiling on small hardware

Not the wire. On a small box the encoder runs out before the link does, and no amount of bandwidth buys the frame back.

And the claim this page can now make

The rate control is a pure function of published state.

No clock, no self, no I/O — every participant computes it independently and arrives at the same answer. There is no negotiation in it anywhere. The function is printed in full below; check by eye that there is no message in it.

@staticmethod
def derive_rate(state, ladder, current=None):
    """The call's rate, from the state alone. Pure: no clock, no self, no IO."""
    senders = state.get("senders") or []
    if not senders:
        return None
    slowest = min(senders, key=lambda s: s["w"] * s["h"]
                  * (s["fps"] if s["fps"] > 0 else REF_FPS))
    i = idx_of(slowest)

    getters = state.get("getters") or []
    worst = ceiling_from(getters)          # the smallest size anybody failed at

    if any(g["struggling"] for g in getters):
        i += 1
    elif getters and all(g["happy"] for g in getters):
        i -= 1
    elif not getters:
        i -= 1

    if worst is not None:
        i = max(i, worst + 1)
    return dict(ladder[max(0, min(len(ladder) - 1, i))])