nomercy-music-player-kmp

The music half of the NoMercy player trio, for Kotlin Multiplatform.

Everything a player does (transport, queue, volume, time, state, plugins, lifecycle) lives in nomercy-player-core-kmp. This library adds only what makes a player a music player, which at the event level is five keys and almost all of them are about crossfade.

That smallness is the point. A listener for play uses CoreEvents.Play on a music player exactly as it does on a video player: one bus, one set of names, and the split is about which library owns the declaration.

Building it

./gradlew build

The build depends on core by its published coordinate and substitutes a sibling ../nomercy-player-core-kmp checkout when there is one, so a change to core is picked up without publishing first.

NoMercy Connect

Connect is music playing across several devices with one of them making sound. A phone, a desktop and a television can all show the same session, and whichever one the server names is the one you hear. The others follow: they show the track and a progress bar that moves, and they never open the stream.

The server decides who is playing. No device decides for itself, because two devices each deciding is how the same song ends up playing twice a fraction of a second apart.

The library owns the protocol and the application owns the wire. You implement MusicConnectChannel over whatever connection you already hold, hand it decoded frames, and the library never sees a hub method name or a JSON key. That split is what lets one plugin serve a phone, a desktop and a television whose transports have nothing in common.

val connect = connectMusic(player, myChannel, screenScope)

// What a device that is not playing should draw.
connect.mirror.collect { render(it.item, it.positionMs, it.durationMs) }

Transport calls stay the same wherever they come from. player.play() on the device that is playing tells the server and carries on, so there is no gap in the audio for the person holding it. The same call on a device that is not playing tells the server and stops there.

	The device you hear	Every other device
A press	reported, then applied here	reported, shown, applied when the server agrees
A frame	reconciled against the engine	drawn, never loaded
Volume	its own remembered level	its own remembered level

Volume is the one thing that is never about who is playing. A phone at thirty percent and a television at eighty are both correct, so each device applies its own remembered level from every frame.

The reference behaviour is the web musicConnectPlugin, and this follows it including the parts that look like corrections: the sequence gate that drops redelivered frames, the shield that holds a press against frames the server sent before it heard about it, and the clock measurement everything about "now" is judged against. The SignalR channel and the retirement of the two older adapters belong to the application and land with app adoption.

Status

The player, the audio backends, the crossfade engine, the event registry and Connect are here and tested. The application wiring that supplies a channel over SignalR is not part of this library.