FFmpeg 8 removed the standalone hardware decoders (h264_videotoolbox/
vaapi/nvdec/d3d11va no longer exist in its configure) — hardware decode
now only exists as a hwaccel attached to the software decoder. The new
oakcodec::hwdecode module therefore opens the regular decoder with the
platform's hardware device context attached (VideoToolbox on macOS,
VA-API then NVDEC on Linux, D3D11VA then NVDEC on Windows): FFmpeg
engages the matching hwaccel, decodes into hardware surfaces, and we
transfer them to system memory (NV12/P010) ahead of swscale.
- HardwareDecoding config switch, default ON by mandate; a checkbox in
Preferences > Rendering (EN/ZH); device creation failure skips to the
next candidate and finally to software; a decode-time failure on a
hardware session reopens it as software and retries once.
- hw_decoder_name() observability hook plus a HW_TRANSFERS counter so
tests can prove the hwaccel really engaged (not silently software).
- Verification: demo.mp4 H.264 decodes through VideoToolbox with a
transferred hardware surface, and the pixels match the software
decode within 0.05; switch off forces software.
- build-ffmpeg.sh also enables nvdec when ffnvcodec headers exist.
Mike-Solar
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