claude-noether
017e27f389
+ meson.build VP8 entries
Net-new VP8 codec dispatcher implemented against
V4L2_CID_STATELESS_VP8_FRAME (kernel UAPI <linux/v4l2-controls.h>:
1900-1958). Single batched control per frame, no init-time device-
wide menus (VP8 has no DECODE_MODE/START_CODE).
Per-frame submission: ONE VIDIOC_S_EXT_CTRLS, count=1, with full
v4l2_ctrl_vp8_frame struct (1232 bytes — corrected vs Phase 2
implicit ~400 estimate; entropy.coeff_probs[4][8][3][11] alone is
1056 bytes).
vp8_set_controls() implements 10 contract clauses per
phase4_iter3_plan.md:
Clause 1: single-control batched submission (count=1)
Clause 2: stack alloc + memset zero (covers all padding)
Clause 3: width/height/version/per-frame scalars; off-by-one
num_dct_parts = num_of_partitions - 1
Clause 4: DPB timestamp resolution (3 refs: last/golden/alt;
NULL surface → 0-sentinel via memset; mirrors iter1
mpeg2.c::pic.forward_ref_ts)
Clause 5: loop filter (6 fields + 3 flag bits; ADJ_ENABLE/
DELTA_UPDATE/FILTER_TYPE_SIMPLE)
Clause 6: quant base + delta derivation from VAAPI's per-segment
absolute index matrix (subtraction recovers signed
deltas; correct for typical content per Phase 5 S1)
Clause 7: segment fields (segment_probs direct copy; flags
assembled with DELTA_VALUE_MODE set unconditionally
per FFmpeg pattern)
Clause 8: entropy table — 3 VAAPI sources merged (Picture: y_mode +
uv_mode + mv_probs; ProbabilityData: coeff_probs[4][8][3]
[11] direct memcpy; IQMatrix: quant)
Clause 9: coder state + first-partition fields + flags assembly
Clause 10: v4l2_set_controls submission
Phase 5 review amendments incorporated:
C1 first_part_header_bits = slice->macroblock_offset
NOT 0 — kernel hantro_g1_vp8_dec.c:260 + rockchip_vpu2_hw_vp8_
dec.c:372 read this field unconditionally to compute the MB-
data DMA offset. Verified via source identity: vaapi_vp8.c:204
and v4l2_request_vp8.c:83 use byte-identical formulas
(8 * (input - data) - bit_count - 8); VAAPI exposes via
slice->macroblock_offset, V4L2 names it first_part_header_bits.
C2 first_part_size = slice->partition_size[0] +
((macroblock_offset + 7) / 8)
VAAPI's partition_size[0] is the REMAINING bytes after parsing
(vaapi_vp8.c:209; va_dec_vp8.h:193-196). Kernel needs the
TOTAL control partition size; recover by adding back ceil
(macroblock_offset/8) bytes.
Phase 3 keyframe verbatim cross-check: 21923 + 819 = 22742 ✓
C4 (int8_t) cast (NOT (s8); s8 is kernel-internal typedef from
<linux/types.h> not exposed to userspace; userspace UAPI
exposes __s8 with double-underscore; portable userspace cast
is int8_t from <stdint.h>).
S3 assert(probability_set) — kernel hantro_vp8.c::hantro_vp8_
prob_update reads coeff_probs unconditionally; NO default-
table fallback. Practical risk low (FFmpeg vaapi_vp8.c always
sends VAProbabilityBufferType per frame), but assert surfaces
immediately if a future consumer doesn't.
Flags assembly: 6 mainline-documented bits only (KEY_FRAME, SHOW_
FRAME, MB_NO_SKIP_COEFF, SIGN_BIAS_GOLDEN, SIGN_BIAS_ALT). EXP +
bit 0x40 NOT replicated despite ffmpeg-v4l2-request-git setting
them on inter frames — kernel hantro_vp8.c only inspects KEY_FRAME
bit. SHOW_FRAME forced unconditional per Phase 3 Q4 (BBB has no
alt-ref invisible frames; documented fidelity gap).
VAAPI inverts: key_frame=0 means it IS a keyframe per VP8 spec.
Backend writes V4L2_VP8_FRAME_FLAG_KEY_FRAME iff
!picture->pic_fields.bits.key_frame.
After this commit alone: vp8.o compiles standalone; meson.build
links it into the shared library. picture.c can't dispatch yet
(commit C wires that).
Refs:
../fresnel-fourier/phase4_iter3_plan.md (10 contract clauses,
Phase 5 amendments
section)
../fresnel-fourier/phase5_iter3_review.md (C1, C2, C3, C4, S3
all incorporated)
../fresnel-fourier/phase3_iter3_baseline.md (verbatim payload
anchors)
references/ffmpeg-kwiboo/libavcodec/v4l2_request_vp8.c (V4L2 ref)
references/ffmpeg-kwiboo/libavcodec/vaapi_vp8.c (VAAPI source ref)
references/linux-mainline/drivers/media/platform/verisilicon/
hantro_g1_vp8_dec.c (RK3399 kernel driver — first_part_header_
bits + first_part_size usage)
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.