Per the correctness-before-speed principle: measure before
optimising. Roadmap going in said "QPU dispatch substitution
to hit 30fps@1080p". Measurement on hertz shows the FFmpeg
software path already hits 65-88 fps@1080p across all three
codecs — QPU substitution would be premature optimisation.
So 8.8 ships what's actually useful:
1. Per-frame timing in test_m2m_stream.
2. Multi-frame AV1 + H.264 streams verified byte-exact at
1080p (closes the "VP9-only stream tests" gap from 8.7).
3. HDR / 10-bit via V4L2_PIX_FMT_P010 + daemon
pack_p010_to_plane.
Test harness (tools/test_m2m_stream.c):
- Per-frame µs timing via CLOCK_MONOTONIC; reports mean/p50/
p99/min/max + wall ms + fps.
- Annex-B H.264 parser: split on 3-/4-byte start codes,
accumulate NALs into access units (push on VCL NAL types
1 or 5). Without AU grouping FFmpeg rejects SPS/PPS-only
buffers as "no frame!".
- Format auto-detect (DKIF magic → IVF; else Annex-B).
- Optional 6th arg `[capture]`: nv12m | p010.
- CAPTURE mmap path generalised for num_planes==1 (P010).
Kernel (kernel/daedalus_v4l2_main.c):
- CAPTURE formats array {NV12M, P010}; enum_fmt walks it.
- daedalus_fill_capture_fmt takes a fourcc:
NV12M: 2 planes, W*H + W*H/2 bytes, bpl=W
P010: 1 plane, W*H*2 + W*H bytes, bpl=W*2
- try_fmt preserves caller fourcc when supported.
- daedalus_complete_resp_frame's dmabuf path now sets each
plane's payload to vb2_plane_size(vb,p) — generalises
cleanly across 1-plane (P010) and 2-plane (NV12M) layouts;
the daemon fully populates the plane so payload =
sizeimage.
Daemon (daemon/src/decoder.c):
- pack_p010_to_plane: YUV420P10LE → P010 single-plane.
10-bit samples shifted left by 6 to MSB-align in 16-bit
words per V4L2 ABI. Y at base+0, interleaved CbCr right
after Y plane (per format spec for single-plane P010).
Strips source stride padding; respects destination stride.
- daedalus_decoder_run_request dispatches on
req->capture_pix_fmt (NV12M → pack_nv12_to_planes; P010
→ pack_p010_to_plane; else warn + skip).
- Includes <linux/videodev2.h> for fourcc constants.
Verification on hertz (Pi 5, 6.12.75+rpt-rpi-2712):
1080p throughput baseline (30 frames testsrc, dmabuf path):
VP9 1080p: mean 12.0 ms, p99 15.9 ms, fps **83.1**, byte-exact ✓
AV1 1080p: mean 15.4 ms, p99 41.0 ms, fps **65.0**, byte-exact ✓
H.264 1080p: mean 11.3 ms, p99 21.5 ms, fps **88.3**, byte-exact ✓
All 2-3× over the 30fps-floor-is-fine criterion.
HDR / 10-bit 1080p P010:
10 frames, 62 MB output, fps **48.8**, byte-exact vs
`ffmpeg -pix_fmt p010le -f rawvideo`.
Small-frame P010 (320×240): fps 966 — fixed daemon overhead
dominates at low resolutions.
v4l2-compliance unchanged from 8.7: 49/49 passing.
Format enumeration confirms NM12 + P010 on CAPTURE.
Clean SIGTERM + rmmod; no kernel oops/WARN.
Roadmap update (docs/roadmap.md):
- 8.8 marked closed with closure-doc reference, including
the explicit "QPU substitution not needed" rationale.
- 8.9 reshaped: libva-v4l2-request consumer integration
(per project_consumer_target memory) — the actual
user-facing endpoint.
Per correctness-before-speed:
- Measured first; QPU work explicitly justified-out via data.
- Byte-exact pixel comparison for every codec/format combo
(NV12: VP9, AV1, H.264; P010: VP9 10-bit at 320×240 and
1080p).
- AU grouping in the Annex-B parser is the correct
semantic boundary, not just a workaround.
- vb2_plane_size for payload generalises to any plane
count, not hardcoded to 2.
Phase 8.9 next: libva-v4l2-request integration — close
the loop from YouTube/Firefox to /dev/video0 + daemon
playback.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
marfrit
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