Flutter Soloud Streaming

Push buffer streaming in flutter_soloud

Push streaming plays audio while it is still arriving: you create an AudioSource with SoLoud.instance.setBufferStream(...), push chunks with addAudioDataStream(source, bytes), and mark the end with setDataIsEnded(source). The engine decodes and buffers internally, auto-pausing when the buffer runs dry and resuming once bufferingTimeNeeds seconds are buffered again. This is the API for icecast/web radio, WebSocket audio, streaming TTS, and generated PCM — not for complete files on disk (use loadFile/loadMem/loadUrl for those).

Minimal example

import 'dart:typed_data';
import 'package:flutter_soloud/flutter_soloud.dart';

Future<void> main() async {
  await SoLoud.instance.init();

  // Synchronous — no await. Returns an AudioSource immediately.
  final stream = SoLoud.instance.setBufferStream(
    maxBufferSizeBytes: 1024 * 1024 * 100, // default: 100 MB cap, not pre-allocated
    bufferingType: BufferingType.released, // free played data (radio-style)
    bufferingTimeNeeds: 2,                 // seconds buffered before unpause
    sampleRate: 44100,
    channels: Channels.stereo,
    format: BufferType.auto,               // detect MP3 / Ogg-Opus / Ogg-Vorbis
    onBuffering: (isBuffering, handle, time) {
      // isBuffering=true: engine paused, waiting for data
      // isBuffering=false: resumed
    },
    onMetadata: (metadata) {
      // AudioMetadata; fires on first data and on mid-stream changes
    },
  );

  // Synchronous too. Safe to call before any data arrives — playback
  // starts once bufferingTimeNeeds seconds are buffered.
  final handle = SoLoud.instance.play(stream);

  // ... as chunks arrive (http stream, WebSocket, generator):
  SoLoud.instance.addAudioDataStream(stream, someUint8ListChunk);

  // When the feed ends (or never, for live radio):
  SoLoud.instance.setDataIsEnded(stream);

  // Optional: know when playback actually finished. Only fires if
  // setDataIsEnded was called.
  stream.soundEvents.listen((event) {
    if (event.event == SoundEventType.handleIsNoMoreValid &&
        event.handle == handle) {
      // finished playing
    }
  });
}

The API shape

All of these live on SoLoud.instance and operate on the AudioSource returned by setBufferStream. Verified against lib/src/soloud.dart and lib/src/enums.dart:

• AudioSource setBufferStream({int? maxBufferSizeBytes, Duration? maxBufferSizeDuration, BufferingType bufferingType = BufferingType.preserved, double bufferingTimeNeeds = 2, int sampleRate = 24000, Channels channels = Channels.mono, BufferType format = BufferType.s16le, bool autoDispose = false, void Function(bool isBuffering, int handle, double time)? onBuffering, void Function(AudioMetadata)? onMetadata}) — synchronous factory. maxBufferSizeBytes and maxBufferSizeDuration are mutually exclusive (asserted); neither pre-allocates memory, they only cap how much data may be added.
• void addAudioDataStream(AudioSource source, Uint8List audioChunk) — push one chunk. Synchronous, callable from any isolate (@pragma('vm:entry-point') functions in the example use it).
• void setDataIsEnded(AudioSource sound) — marks the stream complete. Without this, soundEvents never reports playback completion.
• void resetBufferStream(AudioSource sound) — drops buffered data so you can retune the same source to new content.
• int getBufferSize(AudioSource sound) — current buffered size in bytes.
• Duration getStreamTimeConsumed(AudioSource sound) — elapsed play time; only for BufferingType.released streams (throws for other sounds).
• void setBufferIcyMetaInt(AudioSource sound, int icyMetaInt) — pass the icy-metaint response header of an icecast stream so the engine can strip/extract MP3 or Ogg-FLAC metadata. Must be called once, before the first addAudioDataStream. setMp3BufferIcyMetaInt is a deprecated alias of this.

Key enums (lib/src/enums.dart):

• BufferType — f32le, s8, s16le, s32le are raw interleaved PCM (you must set sampleRate/channels correctly). auto detects MP3, Ogg-Opus, and Ogg-Vorbis containers and ignores sampleRate/channels. opus still exists but is deprecated — it is silently rewritten to auto with a debugPrint.
• BufferingType — preserved: keeps all data in memory, allows multiple simultaneous handles, seeking and looping. released: frees played data (bounded memory for endless feeds), but plays once, cannot seek, and getPosition always returns 0 — use getStreamTimeConsumed instead.

Divergences from audioplayers/just_audio habits:

• No setUrl/AudioSource.uri streaming; you do the HTTP/WebSocket I/O yourself and push raw bytes.
• setBufferStream and play are synchronous — await SoLoud.instance.play(stream) compiles but is pointless; the docs snippet showing that is stale.
• There is no built-in position stream for released streams; poll getStreamTimeConsumed on a timer (the example's buffer_widget.dart does exactly this).
• Buffer underruns are not errors: the engine pauses and fires onBuffering(isBuffering: true, ...), then resumes automatically.

Traps

• BufferingType.released plays exactly once. A second play on the same source throws SoLoudBufferStreamCanBePlayedOnlyOnceCppException. When it finishes, the buffer is empty and you must dispose the source yourself (or pass autoDispose: true).
• getPosition lies for released streams — always Duration.zero. Use getStreamTimeConsumed(sound); calling it on a non-released sound throws.
• Reaching the max buffer size ends the stream. Once the cap is hit, the stream is treated as ended and further addAudioDataStream calls throw SoLoudStreamEndedAlreadyCppException (the web_radio example catches it and reconnects). Size the cap for the feed, or use released.
• Icy metadata ordering. Request the header with Icy-MetaData: 1 on the HTTP request, then call setBufferIcyMetaInt(source, int.parse(headers['icy-metaint'] ?? '0')) on the first audio chunk, before any addAudioDataStream. Later calls are ignored.
• BufferType.opus is deprecated. Passing it still works (rewritten to auto with a debugPrint) but new code should use auto.
• With format: BufferType.auto, sampleRate and channels are ignored — the decoder takes them from the container. They only matter for raw PCM formats.
• Raw PCM must match the declared format exactly: interleaved, little-endian, correct sample rate and channel count; the engine resamples to sampleRate but does not channel-convert or fix wrong formats — mismatch means noise or wrong speed, not an error.
• Compressed streaming needs the bundled Xiph libs. If the app was built with them excluded, addAudioDataStream of compressed data throws SoLoudXiphLibsNotAvailableException.
• Forgetting setDataIsEnded leaves the stream "live" forever: soundEvents never emits handleIsNoMoreValid and (with preserved) the buffer keeps growing.
• maxBufferSizeDuration is computed from sampleRate/channels as ms * sampleRate * channels * 4 bytes (internal float storage) — for auto sources this conversion is approximate.

More depth

• Full recipes (icecast radio with icy metadata, WebSocket PCM, procedural PCM in an isolate): references/recipes.md
• Pull-model streaming (engine requests data via callback; for huge files and byte-range fetching) is covered by the sibling skill flutter-soloud-pull-streaming (skills/flutter-soloud-pull-streaming/SKILL.md).
• Runnable demos in this repo: example/lib/buffer_stream/web_radio.dart, websocket.dart, generate.dart, simple_noise_stream.dart (the last one is the smallest complete example).

Keeping this skill current

This skill ships inside the flutter_soloud package, so upgrading flutter_soloud can carry a newer revision of it than the copy installed in the project. To check, run:

dart run flutter_soloud:skills --check

It reports the installed and bundled skill versions and exits non-zero when an update is available. Offer to update with dart run flutter_soloud:skills (which touches only the skills, never pubspec or build files).