End-to-end edited export — ED.21

The lab's last step was the answer print: the first complete, projectable reel struck from the cut negative — every splice, speed change, and trim finally baked into something you could screen. ED.21 strikes that print. export_edited_project drives the frame generator into the encoder and finalizes a real .mp4.

flowchart LR
  GEN["ExportFrameGenerator\n(retimed BGRA + pts)"] --> PUSH["LiveGstreamerEncoder\n.push_video_frame"]
  PUSH --> FIN["finalize → moov"]
  FIN --> MP4[".mp4"]
  MP4 -.verify.-> DEC["decode back:\ndims + retimed length"]

The encoder is the live recorder's LiveGstreamerEncoder, reused unchanged — the editor's export and the recorder's capture write through the exact same vtenc → h264parse → mp4mux pipeline, so there's one encode path to trust. The export loop is synchronous and polls a cancel flag plus calls an on_progress(done, total) callback once per frame — the hooks the export UI (ED.22) drives. The gst-guarded end-to-end test exports a 2×-speed project and then decodes the result back with EditorVideoStream, asserting the output is a valid container at the source dimensions whose length is the retimed (halved) duration — proof the edit reached the file, verified with our own decoder rather than a brittle byte golden.

The audio rides the same timeline

The generator bakes the visual edits in (trim/split/speed via source_time, the zoom punch-in (ED.16), crop/aspect (ED.15), and background framing (ED.18)). Audio gets the same treatment, with the project's "GStreamer owns the intake; Rust owns the edit arithmetic" split:

flowchart LR
  SRC["source .mp4"] --> DEC["decode_source_audio_f32\n(one gst pass → raw F32LE)"]
  DEC --> RT["retime_audio\n(pure: per-segment trim + speed,\nlinear-interp resample, concat)"]
  RT --> PUSH["encoder.push_audio_chunk"]
  PUSH --> REMUX["finalize remux (build_remux_args)"]
  REMUX --> MP4[".mp4 — video + retimed audio"]

One gst-launch pass decodes the whole source audio to raw interleaved F32LE; retime_audio then slices it in pure Rust — for each segment, the source sample-frame range resampled to that segment's project duration (a 2× segment emits half the sample-frames; linear interpolation keeps it click-free) — and the result feeds the encoder's audio scratch, so the recorder's existing finalize remux muxes it onto the retimed video. The end-to-end test builds an audio-bearing source and proves the export carries a retimed audio track.