Real MP4 → wisp playback

This is the first chunk that puts the complete data path together:

sequenceDiagram
    participant File as sample.mp4
    participant Discoverer as gst-discoverer-1.0
    participant Launch as gst-launch-1.0<br/>(filesrc → decodebin →<br/>videoconvert → BGRA → fdsink)
    participant Stream as GstreamerPipeStream<br/>(impl VideoStream)
    participant Player
    participant Texture as VideoTexture
    participant Renderer as wisp::Sprite +<br/>Renderer
    participant Output as RenderTexture → PNG

    File ->> Discoverer: probe
    Discoverer -->> Player: width / height / fps / duration
    File ->> Launch: decode
    Launch -->> Stream: raw BGRA bytes on stdout
    Stream ->> Player: next_frame() → VideoFrame
    Player ->> Texture: upload_bgra(frame)
    Player ->> Renderer: render_stage(stage)
    Renderer ->> Output: read_pixels → PNG

How to run

The committed test fixture ships with the repo, so the example is runnable with no setup beyond brew install gstreamer:

cargo run -p playback --example play_file

Custom video:

cargo run -p playback --example play_file -- /path/to/video.mp4

Output (running against tests/fixtures/sample.mp4)

The fixture is the M-DEC.1 mock-stream gradient, encoded once with x264 into an 11 KB MP4. The example pulls it back through GStreamer + Player

• wisp and writes one PNG per render-tick where a frame was uploaded.

Tick 00	Tick 01	Tick 02	Tick 03

Tick 04	Tick 05	Tick 06

The first tick pulls two frames (catch-up — t=0 and t=1/30 s are both due before the wallclock has advanced past either), then it settles to one frame per tick. The Player exits to Ended cleanly when the GStreamer pipe returns EOF.

Why GStreamer (and why CLI not crate)

GStreamer is LGPL and modular: decodebin auto-selects the best codec plugin for the file, including hardware decoders (vtdec on macOS, vah264dec on Linux, nvh264dec with NVIDIA). Switching backends never touches our code.

The CLI-pipe approach trades a fork for zero compile-time integration. For the player loop that's one fork for the whole stream, not per-frame — overhead is amortised. The Rust-bound integration (gstreamer-rs) is queued as M-DEC.3+; the VideoStream trait makes that swap a one-line change at the call site.

What's now possible

With this chunk landed, the recorder has 4 of 6 stages on the path to "first MP4 plays in Tauri-Leptos via wisp":

• ✅ M-DEC.1 — VideoStream trait + MockVideoStream
• ✅ M-PLAY.1 — Player state machine + frame pump
• ✅ M-DEC.2 — GstreamerPipeStream (real MP4 decode)
• ✅ M-INT.1 — Trunk + Leptos in Tauri (replace the vanilla JS frontend)
• ✅ M-INT.2 — Tauri serves Trunk bundle + OS file-drop wiring
• ✅ M-PREVIEW.1 — Native winit sibling window with the wisp surface
• ✅ M-PLAY.2 — Tauri↔player IPC for transport controls

GstreamerPipeStream · Player · Decode overview · Player overview