claude-noether
65969da3ee
Anchors campaign-wide claims with measured numbers. Runs four consumer configurations against $FIXTURE for $DURATION seconds each: 1. mpv --hwdec=vaapi (DMA-BUF zero-copy through libva) 2. mpv --hwdec=vaapi-copy (HW decode + VAImage readback) 3. firefox (iter5-amend, sandbox enabled, file:// URL) 4. mpv --hwdec=no (SW decode baseline / control) Captures per consumer: CPU% (median + p90 from pidstat), GPU freq median (from /sys/class/devfreq/fde60000.gpu/cur_freq, polled at 100ms cadence), drops in window (from mpv --term-status-msg), p50 frame interval (mpv only), VmRSS delta (from /proc/PID/status). Emits a markdown table with raw numbers per consumer — no aggregation, no improvement ratios, no curated-benchmark framing. Honest schema including '—' for measurements not available per consumer (e.g. Firefox drops without internal hooks). Phase 5 sonnet review caught 3 issues, all addressed before commit: 1. pidstat $8 column heuristic — replaced with header-driven %CPU field detection (robust across sysstat 12.x point releases) 2. GPU freq median computation used /dev/stdin in nested subshell- over-pipe (unreliable) — replaced with temp-file path 3. --frames=$((DURATION * 30)) hardcoded 30fps (fixture-hardcoding per feedback_no_fixture_hardcoding.md) — replaced with --length=$DURATION (wall-time bounded, framerate-agnostic) Plus minor: empty cpu_pct.log now emits ERR rather than silent 0, distinguishing measurement failure from "process used no CPU." Reproducibility surface: run date, host, kernel, driver sha256, fixture path+size, duration captured in the output markdown. Hardware constants (/dev/video1, /dev/media0, devfreq path, driver install path) are documented as PineTab2 (RK3566 via hantro/rk3568-vpu) specific. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
v4l2-request libVA Backend
About
This libVA backend is designed to work with the Linux Video4Linux2 Request API that is used by a number of video codecs drivers, including the Video Engine found in most Allwinner SoCs.
Status
The v4l2-request libVA backend currently supports the following formats:
- MPEG2 (Simple and Main profiles)
- H264 (Baseline, Main and High profiles)
- H265 (Main profile)
Instructions
In order to use this libVA backend, the v4l2_request driver has to
be specified through the LIBVA_DRIVER_NAME environment variable, as
such:
export LIBVA_DRIVER_NAME=v4l2_request
A media player that supports VAAPI (such as VLC) can then be used to decode a video in a supported format:
vlc path/to/video.mpg
Sample media files can be obtained from:
http://samplemedia.linaro.org/MPEG2/
http://samplemedia.linaro.org/MPEG4/SVT/
Technical Notes
Surface
A Surface is an internal data structure never handled by the VA's user containing the output of a rendering. Usualy, a bunch of surfaces are created at the begining of decoding and they are then used alternatively. When created, a surface is assigned a corresponding v4l capture buffer and it is kept until the end of decoding. Syncing a surface waits for the v4l buffer to be available and then dequeue it.
Note: since a Surface is kept private from the VA's user, it can ask to directly render a Surface on screen in an X Drawable. Some kind of implementation is available in PutSurface but this is only for development purpose.
Context
A Context is a global data structure used for rendering a video of a certain format. When a context is created, input buffers are created and v4l's output (which is the compressed data input queue, since capture is the real output) format is set.
Picture
A Picture is an encoded input frame made of several buffers. A single input can contain slice data, headers and IQ matrix. Each Picture is assigned a request ID when created and each corresponding buffer might be turned into a v4l buffers or extended control when rendered. Finally they are submitted to kernel space when reaching EndPicture.
The real rendering is done in EndPicture instead of RenderPicture because the v4l2 driver expects to have the full corresponding extended control when a buffer is queued and we don't know in which order the different RenderPicture will be called.
Image
An Image is a standard data structure containing rendered frames in a usable pixel format. Here we only use NV12 buffers which are converted from sunxi's proprietary tiled pixel format with tiled_yuv when deriving an Image from a Surface.