claude-noether
406d08e122
VP9 codec dispatcher implementing 12 contract clauses against
V4L2_CID_STATELESS_VP9_FRAME (0xa40a2c) +
V4L2_CID_STATELESS_VP9_COMPRESSED_HDR (0xa40a2d). 2 batched
controls per frame; rkvdec on RK3399 mandatorily requires both
per drivers/staging/media/rkvdec/rkvdec-vp9.c::rkvdec_vp9_run_preamble:752.
Implementation:
- ~80 LOC VPX range coder (vp9_rac_*) — minimal port of FFmpeg
vpx_rac.[ch] + vp89_rac.h. Stateless static helpers.
- inv_map_table[255] + read_prob_delta — verbatim copy from
v4l2_request_vp9.c:44-97.
- vp9_parse_uncompressed_header_lf_quant — partial parse for the
fields VAAPI doesn't expose: lf_delta_enabled / lf_delta_update /
lf_ref_delta[4] / lf_mode_delta[2] / base_q_idx /
delta_q_y_dc / delta_q_uv_dc / delta_q_uv_ac. ~120 LOC.
- vp9_fill_compressed_hdr — port of FFmpeg fill_compressed_hdr
with Phase 5 C3 out_reference_mode parameter. ~140 LOC.
- vp9_set_controls — orchestrates Clauses 1+2+4+5+7+10+11+12.
~120 LOC.
Phase 5 amendments incorporated in code:
- C1: frame.interpolation_filter = direct from VAAPI's
mcomp_filter_type (NO XOR; vaapi_vp9.c:62 already applied it
before storing into VAAPI's mcomp_filter_type).
- C2: persistent vp9_lf state added to object_context (in
context.h). Initialized to VP9 spec defaults
{1,0,-1,-1,0,0} on keyframe / intra_only / error_resilient.
Updated only when parser sees lf_delta.update=1. Always
copied to kernel control.
- C3: vp9_fill_compressed_hdr takes uint8_t *out_reference_mode;
threaded through call site. allowcompinter derived from VAAPI
sign-bias bits.
Phase 5 S4: uv_mode memcpy from FFmpeg's fill_compressed_hdr
omitted — rkvdec reads uv_mode from kernel's persistent
probability_tables, NOT from prob_updates ctrl.
Clause 3 compile-time _Static_assert on struct sizes (168/2040)
matches Phase 3 empirical baseline; UAPI shifts will fail loudly.
surface.h: extends params union with vp9 { picture, slice }.
context.h: adds vp9_lf { ref_deltas[4], mode_deltas[2], initialized }.
meson.build: adds vp9.c + vp9.h.
Build: clean on fresnel (linux-fresnel-fourier 7.0-1, libva 1.23).
Runtime: not yet wired in picture.c — next commit.
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.