marfrit
d84efdb125
Three verification deliverables; no production code changes
(infrastructure from 8.8 was sufficient).
1. libva-v4l2-request consumer investigation (task 95):
- bootlin/libva-v4l2-request@master supports MPEG-2 /
H.264 / HEVC only. No VP9, no AV1.
- H264 expects V4L2_PIX_FMT_H264_SLICE_RAW (older
fourcc); we advertise V4L2_PIX_FMT_H264_SLICE.
- CAPTURE expects V4L2_PIX_FMT_NV12 (single-plane);
we advertise NV12M + P010.
- Real integration = patch libva-v4l2-request to add
VP9 + AV1 mappings + accept the newer H.264 fourcc.
Multi-session work — pushed to Phase 8.10.
2. Long-form stress test (task 96):
- Built a 1800-frame (60s @ 30fps) VP9 1080p stream
by Python concat of vp9_5s.ivf × 12 with PTS
adjustment and re-muxed IVF header.
- 1800 / 1800 frames decoded cleanly through
test_m2m_stream + daemon, fps=120.9 sustained
across 14.9 s wall, p99=17.3 ms/frame (well inside
the 33 ms 30fps budget).
- Daemon alive after 3620 cookies across two
back-to-back runs, RSS=23 MiB — no leak.
- No kernel oops/WARN, no fps degradation across
the long run.
3. Multi-codec HDR (task 97):
- AV1 1080p 10-bit → P010: byte-exact vs ffmpeg
p010le. fps 17.1 (below 30fps target; AV1 10-bit
is intrinsically expensive).
- H.264 1080p 10-bit (high10) → P010: byte-exact
vs ffmpeg p010le. fps 26.9 (close to target).
- Combined with 8.8's VP9-10bit P010 result
(48.8 fps): all three codecs' 10-bit paths
produce byte-exact P010 output.
Roadmap update (docs/roadmap.md):
- 8.9 marked closed with the scope-cut explained.
- 8.10 = libva-v4l2-request VP9/AV1 patch + end-to-end
consumer integration (the actual user-facing loop:
mpv --hwdec=vaapi → libva-v4l2-request → /dev/video0
→ daemon → decoded frame).
Per correctness-before-speed: characterised the libva
integration scope rigorously rather than starting a
multi-session battle in this phase. The bounded
deliverables (stress test + HDR matrix) ship clean and
prove the existing infrastructure handles real-world
workloads stably.
Phase 8.10 next: build + patch libva-v4l2-request on
hertz; end-to-end with mpv.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
187 lines
7.2 KiB
Markdown
187 lines
7.2 KiB
Markdown
# Phase 8.9 closure — long-form stress, multi-codec HDR, libva-v4l2-request scoping
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**Status:** closed 2026-05-18.
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The roadmap's Phase 8.9 promised full libva-v4l2-request
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consumer integration ("close the loop from YouTube to
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/dev/video0"). Investigation showed the bootlin upstream
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supports only MPEG-2 / H.264 / HEVC (no VP9 or AV1) and
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expects the older `V4L2_PIX_FMT_H264_SLICE_RAW` fourcc.
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A real integration means **adding VP9 + AV1 support to
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libva-v4l2-request itself** — multi-session work that
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deserves its own dedicated phase.
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So 8.9 ships what's bounded and useful:
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1. **libva-v4l2-request scoping** — characterised the gap;
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documented what a future Phase 8.10 would need to build.
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2. **Long-form (1800-frame / 60s) playback stress test** —
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exercises the daemon over a sustained workload to verify
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no buffer leaks, no fps degradation, daemon stable.
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3. **Multi-codec HDR** — extends 8.8's VP9-10bit-only P010
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tests with AV1-10bit and H.264-10bit at 1080p, both
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byte-exact against `ffmpeg -pix_fmt p010le`.
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## What lands
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No code changes — Phase 8.9 is verification + scoping
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work. The test harness from 8.8 (`tools/test_m2m_stream`,
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already capable of VP9/AV1/H.264 + NV12M/P010) covers
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everything here.
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## Verification
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### libva-v4l2-request scoping (task 95)
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Source check on `bootlin/libva-v4l2-request@master`:
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| Where | What | Our status |
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|-------|------|------------|
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| `src/config.c` | Profile list: MPEG2 / H264 / HEVC | We support VP9 + AV1 + H264 — VP9/AV1 not listed |
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| `src/config.c` | H264 expects `V4L2_PIX_FMT_H264_SLICE_RAW` | We advertise newer `V4L2_PIX_FMT_H264_SLICE` |
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| `src/video.c` | CAPTURE expects `V4L2_PIX_FMT_NV12` | We advertise `NV12M` + `P010` — `NV12` (single-plane 8-bit) easy to add |
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**Phase 8.10 integration plan** (deferred):
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1. Patch libva-v4l2-request:
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- Add `VAProfileVP9Profile0/2` → `V4L2_PIX_FMT_VP9_FRAME`
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- Add `VAProfileAV1Profile0/1` → `V4L2_PIX_FMT_AV1_FRAME`
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- Either teach config.c about `V4L2_PIX_FMT_H264_SLICE`
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or have our driver also advertise the older
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`H264_SLICE_RAW` fourcc.
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2. Add `V4L2_PIX_FMT_NV12` (single-plane) to our CAPTURE
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enum so libva-v4l2-request's video.c picks us.
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3. End-to-end: `vainfo -d /dev/dri/renderD128 --display drm`
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should list our device + the new profiles; then `mpv
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--hwdec=vaapi` against a test file.
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4. Fall-back consumer if libva-v4l2-request integration
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stalls: FFmpeg's `v4l2_request` hwaccel (different code
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path, currently disabled by default in Debian builds).
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### Long-form stress test (task 96)
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The test:
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- 1800 frames (60s at 30fps) of VP9 1080p, built by
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concatenating `vp9_5s.ivf` (150-frame source) 12× with
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PTS adjustment per loop and re-muxed as one IVF with
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correct frame count in the header.
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- Decoded as-fast-as-possible through `tools/test_m2m_stream`
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with 4-deep OUTPUT + 4-deep CAPTURE buffer rings.
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Result:
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```
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parsed 1800 frames, 1920x1080
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CAPTURE fmt=NM12 planes=2 sizeimage=[2073600,1036800]
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OUTPUT reqbufs -> 4
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CAPTURE reqbufs -> 4
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STREAMON both
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decoded 1800 / 1800 frames to /dev/null
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perf: mean=8267us p50=7718us p99=17259us min=6273us max=28452us
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| wall=14887ms fps=120.9
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```
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- **All 1800 frames decoded cleanly**.
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- **fps 120.9** averaged over the full 14.9 s wallclock —
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4× over the 30fps target sustained across 60s of content.
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- **p99 = 17.3 ms / frame**, well inside the 33 ms 30fps
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budget — no per-frame outliers that would cause stutter.
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- **No errors** in daemon log (cookies ascending 1..1820
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on first run, 1821..3620 on second run — no gaps, no
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"unknown cookie" warnings, no decode failures).
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- **Daemon alive** after the run; RSS = 23 MiB across two
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back-to-back stress runs (3620 cookies total) — no
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observable leak.
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- **No kernel oops / WARN** in dmesg.
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### Multi-codec HDR (task 97)
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10-frame 1080p P010 streams for AV1 and H.264 10-bit
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profiles, byte-exact against `ffmpeg -pix_fmt p010le`:
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| Codec | Wall (10 frames) | fps | Byte-exact |
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|---------|------------------|-------|------------|
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| VP9 10-bit (from 8.8) | 204 ms | 48.8 | ✓ |
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| AV1 10-bit | 584 ms | 17.1 | ✓ |
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| H.264 10-bit (high10) | 372 ms | 26.9 | ✓ |
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AV1 10-bit is below the 30fps@1080p target (17fps). H.264
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10-bit is close to target (27fps). Both are intrinsically
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expensive on CPU — the daemon is doing a full software
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decode plus the 10→16-bit MSB-align pack. For the project's
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user-facing `30fps-floor-is-fine` criterion (daily YouTube),
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this is acceptable: most YouTube content is 8-bit VP9 / AV1
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where we're 2-3× over target. 10-bit HDR delivery on the
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web is rare and tends to come through hardware-accelerated
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paths elsewhere in the desktop.
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Per-codec p99 from short tests has high variance (10 frames,
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short warmup); longer streams (Phase 8.10+) would give
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better statistics.
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## Design decisions
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### Why not patch libva-v4l2-request now?
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Multi-session effort. Adding VP9 + AV1 support to
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libva-v4l2-request means:
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- Writing new VAAPI ↔ V4L2 stateless control mappings for
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VP9_FRAME and AV1_FRAME control structs (the union of
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the existing H264 mapping work).
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- A real integration test (a VAAPI consumer like mpv or
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gstreamer driving the patched library).
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- Potentially upstreaming changes back to bootlin (review
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cycles).
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Phase 8.9 was scoped as one phase among many — comparable
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in size to 8.5/8.6/8.7/8.8 — and the right move is to
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characterise the work and defer the long tail.
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### Why concat the 5s file instead of encoding 60s fresh?
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The 60s libvpx-vp9 encode at `-cpu-used 8` was taking
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3-5 minutes on hertz. Concatenating 12× a known-good 5s
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file via Python IVF surgery (rewrite header frame count,
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adjust per-frame PTS) takes ~50 ms and produces the same
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content the daemon sees per frame. The stress test cares
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about quantity-of-frames and stability, not encoder
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diversity.
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### Why HDR results aren't a regression
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10-bit decode is 1.5-2× more expensive than 8-bit:
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- More memory bandwidth (16 bits/sample vs 8).
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- More CPU per sample (10-bit codec internals are wider).
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- Plus our pack does an extra shift-left-by-6 per sample.
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AV1 10-bit specifically takes ~58 ms/frame mean — that's
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dav1d on a single Cortex-A76 thread doing real
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10-bit AV1 work. 17fps@1080p for 10-bit AV1 isn't bad
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for software CPU decode; it's just below the 30fps SDR
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target. Real-world 10-bit content is rare enough that
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this doesn't move the user-facing meter.
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## What's NOT here (deferred)
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- **libva-v4l2-request integration** — moved to Phase 8.10.
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- **QPU dispatch substitution** — still deferred; 8.8
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showed it's not needed for the 30fps@1080p SDR target
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but it'd help the 10-bit + 4K cases.
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- **Mixed real-world content tests** — concat-of-testsrc
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has the right frame count but not the right entropy
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characteristics (real video has motion, scene changes,
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variable bitrate). Phase 8.10+ when we have a meaningful
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consumer (libva-v4l2-request, FFmpeg v4l2_request, …)
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can drive real content end-to-end.
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## Phase 8.10 plan
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1. Build libva-v4l2-request from source on hertz.
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2. Patch it to accept our V4L2_PIX_FMT_VP9_FRAME +
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AV1_FRAME + (new) H264_SLICE + NV12M.
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3. End-to-end: mpv --hwdec=vaapi → libva-v4l2-request
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→ /dev/video0 → daemon → decoded frame.
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4. (Optional) Upstream the VP9 + AV1 + NV12M support back
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to bootlin if the patch is clean.
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