Media playback

Audio and video playback in Firefox spans multiple subsystems: HTMLMediaElement, MSE / EME, decoders (in the RDD process), graphics integration, and WebRTC.

Layers

graph TD
    Element[HTMLMediaElement] --> Decoder[ChannelMediaDecoder<br/>or MediaSourceDecoder]
    Decoder --> Reader[MediaFormatReader]
    Reader --> RDD[RDD process<br/>platform decoders]
    RDD --> Frames[Decoded frames]
    Frames --> Sink[VideoSink / AudioSink]
    Sink --> Compositor[GPU compositor for video]
    Sink --> Audio[Cubeb audio backend]

Directories

• dom/media/ — main implementation. Contains MediaSource, EME, WebRTC platform glue, MSE, and the demuxer/decoder framework.
• media/audioipc/ — audio IPC (Rust).
• media/libcubeb/ — vendored cubeb (cross-platform audio).
• media/libavif/, media/libdav1d/ — AVIF / AV1.
• media/libopus/, media/libvorbis/, media/libtheora/, media/libvpx/ — codec libraries.
• media/openmax_dl/ — DSP primitives.
• media/webrtc/ — WebRTC (libwebrtc fork).

EME

Encrypted Media Extensions (Widevine / PlayReady) are dispatched through the GMP (Gecko Media Plugin) process, an OOP host for closed-source CDM binaries. See dom/media/gmp/.

Related

• DOM
• Process model
• Graphics