State and streams topic

Read what the player is doing, and react when it changes.

State and stream

The player shows its state in two ways:

• player.state is an immutable snapshot that you read synchronously.
• player.stream holds one stream per value, for StreamBuilder or listen().

// Read once, in a handler or in build()
final volume = player.state.settings.volume;

// Follow every change
player.stream.volume.listen((v) => print('volume $v'));

// Wait for the next change only
final next = await player.stream.volume.skip(1).first;

A state stream gives each new listener the current value first, then every change. A StreamBuilder on it needs no initialData:

StreamBuilder<Duration>(
  stream: player.stream.position,
  builder: (context, snapshot) => Text('${snapshot.data}'),
);

Event streams, such as endFile, error and log, deliver only what happens after listen().

The snapshot holds its values in six groups:

Group	What it holds
state.playback	transport, position and the playlist
state.network	buffering, cache and read health of the source
state.file	what mpv read from the current file: tags, tracks, cover, paths
state.output	the audio output in use and its format
state.settings	what the app asked: volume, speed, effects, output, network
state.versions	the libmpv and FFmpeg versions

The streams stay flat: player.stream.position follows state.playback.position. The flat fields of 0.6, such as state.position, still read the same values, deprecated until 0.8.0.

A few values live on one side only. playbackState, prefetchState, prefetchCacheDuration, waveform, loudnessScan and the event streams, fft, pcm and loudnessMeter among them, have no field in state. tlsCaFile, readError and skippedSegments have no stream.

Current entry

final s = player.state;

// index is -1 while openAll still builds the queue
final i = s.playlist.index;
if (i >= 0 && i < s.playlist.items.length) {
  print(s.playlist.items[i].uri);
}

Playback state

playbackState folds playing, buffering, completed, pausedForCache and the loaded file into one value, for a single indicator.

player.stream.playbackState.listen((phase) {
  switch (phase) {
    case MpvPlaybackState.idle:      // no file loaded
    case MpvPlaybackState.loading:   // a file opens
    case MpvPlaybackState.buffering: // waits for the network during playback
    case MpvPlaybackState.playing:   // produces audio
    case MpvPlaybackState.paused:    // a file is loaded, no audio
    case MpvPlaybackState.completed: // the last entry ended, no loop on
  }
});

A paused live stream is paused, not idle.

Which flag to use

Value	Use it for
playWhenReady	The play and pause button. Seeks and buffering leave it unchanged
playing	A spinner. It turns false during seeks and buffering
playWhenReady && playing	Audio comes out now
completed	The end of the last entry. It stays false between entries and while a loop is on
buffering	A file opens. A stall during playback shows on pausedForCache
cacheBufferingState	A buffering indicator, from 0 to 100

bufferingPercentage compares the cache with state.settings.cache.secs. It stays near 0 with the default cache size, so prefer cacheBufferingState or bufferDuration against your own target.

duration is Duration.zero for a live stream and while it is unknown. When FFmpeg estimates it from the bitrate (an MP3 without a Xing header, ADTS AAC, a length a server guessed), it can be far off: durationEstimated is then true. A Media.waveformDurationHint of the entry takes the estimate's place, and durationEstimated is false with it. position updates at most about 30 times a second.

Streams

Group	Some streams	What for
Playback	position, duration, volume, rate, pitch, seeking	Controls and the progress bar
Playlist and tracks	playlist, loop, shuffle, tracks, chapters	The queue and its entries
Output	audioDevice, audioDevices, audioParams, audioOutParams, systemVolume	Devices and the format that plays
Effects	audioEffects, replayGain, gapless	The effects chain
Network and cache	cache, pausedForCache, cacheSpeed, demuxerCacheState	Buffering and download speed
File	metadata, coverArt, mediaTitle, fileFormat, fileSize, path	Tags and file details
Timing	audioPts, timeRemaining, playtimeRemaining	Time left, with or without the rate
A-B loop	abLoopA, abLoopB, abLoopCount, remainingAbLoops	The loop section
Analysis	fft, pcm, waveform, loudnessScan, loudnessMeter	Visualizers and meters
Media session	mediaSession, mediaSessionCommands	The OS controls
Events	seekCompleted, endFile, error, log, internalLog, hook	Things that happen once

Most setters have a stream of the same name, so setRate changes rate. The API reference of PlayerStream and PlayerState lists every value with its docs.

A null field means the value is missing, and the field's docs say what that means. systemVolume is null on an output without a system volume, abLoopCount is null for an endless loop, and readError is null while completed is false.

abLoopA and abLoopB are null while that point is off. They return to null when the file they were set on ends. A point set with no file loaded stays for every file.

See the Errors and logs, Visualizer and analysis and Media session topics for the event streams.

Prefetch

With setPrefetchPlaylist(true), the player opens the next entry in the background before the current one ends. prefetchState follows that work. See the Playback topic to set up prefetch.

State	Meaning
idle	No prefetch runs
loading	The next entry opens and fills its cache
ready	The next entry is open, and the next change of entry uses it
used	The entry started from the prefetch. It stays until the next loading, or until a cancel resets it to idle
failed	The next entry could not open. It stays until the next loading or a stop

player.stream.prefetchState.listen((state) {
  if (state == PrefetchState.failed) print('Prefetch failed');
});

// How much of the next entry is cached, zero while nothing is prefetched
player.stream.prefetchCacheDuration.listen((buffered) {
  const target = Duration(seconds: 30);
  final progress = (buffered.inMilliseconds / target.inMilliseconds).clamp(0.0, 1.0);
  showPrefetchProgress(progress);
});

Classes

FileState

What mpv read from the current file: its tags, tracks, chapters, cover, format and paths. Reset when nothing is loaded.

LibraryVersions

The versions of the libmpv and FFmpeg the player runs on.

NetworkState

Buffering, cache and read health of the current source: what mpv holds ahead and how the transport is doing.

OutputState

The audio output in use: its device, the format it plays and its state, and the system mixer when the output has one.

PlaybackState

Transport, position and the playlist of the Player: what plays, where it is, and how it moves through the queue.

PlayerSettings

What the app asked of the player: volume and speed, the effects and the analysis, the output it wants, the network and the media session.

PlayerState

Immutable snapshot of the Player's complete playback state, in six groups: playback, network, file, output, settings and versions.

PlayerStream

Typed streams of the Player's state and events.