[c4software]

The client exported its VA-API decode surfaces to Vulkan only after the first decode of a stream. On libva-v4l2-request (Apple AVD on Asahi, libva-v4l2_request-avd), the first decode fixes how the CAPTURE queue is backed: MMAP when the surface has not been exported yet. Every surface exported afterwards gets its own standalone dma-buf, and the driver then refuses to decode into it:

libva-v4l2request: cannot decode into the already-exported surface layout

This happened from the second frame of every stream, so it repeated on each --headless resize, on both the main and aux streams.

H264Decoder now exports every surface when it opens a stream, before any decode, and keeps the descriptors. DecodeStream imports those instead of exporting after the fact. The driver supports this order: it switches the queue to DMABUF mode and decodes into the exported memory (the same order Chromium uses). On AMD and Intel the same dma-buf is exported, just earlier.

Testing

• scripts/check.sh passes.
• Asahi (MacBook, libva-v4l2_request-avd 1.3.r11, kernel 7.2.11) as the client, --headless against an AMD server: the errors are gone. The driver logs surface ... was exported before its first decode; decoding into client-exported dma-bufs, and resizing the window reopens the stream at each new size (1920x1088, 768x832, 960x1120, ...).
• scripts/e2e.sh has not been run.

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The changes appear safe to merge; no actionable code issues were found.

Summary

The decoder now exports every VA-API surface when it opens a stream, before submitting any decode.

• VA-API surfaces are exported before each stream's first decode.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Open stream] --> B[Allocate VA-API surfaces]
  B --> C[Export and keep descriptors]
  C --> D[Submit first decode]
  D --> E[Import saved descriptors into Vulkan]
  E --> F[Wait for decode and recombine]

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_{Reviews (1) · Last reviewed commit: "Export decoder surfaces before the first..." · Reviewed by Greptile}