Makes the common Linux H.264 export fully GPU-resident: decode (HW NV12) →
composite → VAAPI encode all on one device, no CPU round-trips.
- gpu-video-encoder: ZeroCopyEncoder now holds wgpu (device,queue,adapter) handles
instead of owning a DrmDevice. New `new_on_device(device,queue,adapter,...)` runs
the RGBA→NV12 render + DMA-BUF import on a passed device; `new` keeps building its
own. The encoder only *imports* VAAPI surfaces (not export), so the shared
import-capable device works directly.
- editor: stash the shared device handles on EditorApp (set in the creation closure
from the eframe render_state when the shared device is active) and thread them
through start_video_export / start_video_with_audio_export → try_build_zero_copy,
which uses new_on_device when available. ZeroCopyVideo carries on_shared_device →
the export composite uses hardware_ok=true (consuming HW-decoded GPU frames from
pt 1) only then.
Falls back to the own-device encoder (decode downloads to CPU) when no shared
device. Tradeoff: the export now shares the GPU with the UI thread (was a separate
device); acceptable for the GPU-resident-decode win. Compiles; crate tests build.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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