Audio & Media
Sound and video both decode compressed PSP formats and feed them to browser APIs.
Audio (src/audio/)
| File | Contents |
|---|---|
audio-engine.ts | AudioEngine, AudioContext + AudioWorkletNode, channel mixing |
atrac-decoder.ts | ATRAC3+ decode functions (decodeAtrac, warmupAtracDecode, parseAtracHeader, ...) via @ffmpeg/ffmpeg (WASM) |
audio-worklet-processor.ts | the AudioWorklet script (runs off the main thread) |
The PSP has 8 regular PCM audio channels (indices 0-7), a separate SRC channel (index 8, used by sceAudioSRC* with its own sample rate), and a single shared Output2 stereo channel (index 9). AudioEngine reserves/releases channels and queues PCM submitted by the sceAudio* HLE handlers; the AudioWorklet mixes all channels to stereo at the PSP-native 44.1 kHz and plays them through Web Audio.
ATRAC3+ (the PSP's compressed audio) is decoded by module-level functions in atrac-decoder.ts (decodeAtrac, parseAtracHeader) using a bundled @ffmpeg/ffmpeg (WASM) build. Decode is asynchronous (Promise-based), so the sceAtrac* handlers return their result in a follow-up step. warmupAtracDecode() pre-heats the ffmpeg pool before gameplay so the first decode doesn't stall.
Wall-clock audio
Audio output is paced by the Web Audio hardware clock, not the emulated cycle clock. In a save state the audio context isn't serialized; playback resumes from the restored channel/decode state, which may produce a tiny blip.
Media / Video (src/media/)
| File | Contents |
|---|---|
mpeg-decoder.ts | MpegMediaDecoder, H.264 decode via WebCodecs |
psmf-demux.ts | PsmfDemux, streaming MPEG-2 Program Stream demultiplexer |
psmf-decoder.ts | PsmfDecoder, H.264 decode helpers (WebCodecs) |
PSP cutscenes are H.264 inside an MPEG Program Stream (PSMF). The demuxer is streaming: the game feeds Program Stream bytes incrementally through the sceMpeg ringbuffer, and PsmfDemux splits out H.264 access units as the bytes arrive (cheap byte work). The decoder then decodes frames lazily on demand via the browser's VideoDecoder (WebCodecs), keeping a small lookahead. This avoids racing hundreds of frames ahead when a game fills its ringbuffer in one burst.
The sceMpeg* and scePsmfPlayer* HLE handlers (hle-media.ts, hle-mpeg.ts, hle-psmf-player.ts) drive these, and the frontend's pmf.ts plays opening movies.
Browser only
WebCodecs is not available in Node, so video decode only works in the browser. A mid-stream seek may glitch a single frame across a save-state restore, since the VideoDecoder's internal state can't be serialized.