claude-noether
692eaa0053
Root cause for VP9 criterion-4 failure traced via runtime instrumentation: context.c:194 unconditionally set context_object->h264_start_code = true for every CreateContext, regardless of codec profile. picture.c:70 then prepends 0x00 0x00 0x01 (ANNEX-B start code) to ALL slice data including VP9 frames. VP9 has no start codes — its uncompressed_header begins with the raw frame_marker byte (0x10 in the high 2 bits). The 3-byte prefix shifted the rkvdec driver's bitstream-read by 24 bits, producing a silent decode failure (frame_marker mismatch -> driver fails to locate a valid frame -> CAPTURE slot stays at cap_pool init pattern, the dim 0x4c green visible in Phase 7 hwdownload PNGs). iter4 fix: switch on config_object->profile in RequestCreateContext. Set h264_start_code = true only for VAProfileH264* and VAProfileHEVCMain. False for MPEG2/VP8/VP9. iter1 (MPEG-2) and iter3 (VP8) had this same bug latent — they passed because their criterion-4 verification used different paths (iter1 direct readback was small enough to mask, iter3 used transitive proof not pixel comparison). The Phase 7 byte-level pixel comparison is what exposed it. Empirical proof of the fix on fresnel: - pre-fix submission FRAME control bytes 0-23: lf.flags=0x01 (only DELTA_ENABLED), base_q_idx=0x41 — bit-misaligned because parser was reading the prefix bytes. - post-fix submission FRAME control bytes 0-23 byte-match Phase 3 kernel-direct anchor: lf.flags=0x03 (ENABLED|UPDATE), base_q_idx=0x2e (46). Transitive-proof leg 1 (backend-payload == kernel-direct-payload) satisfied for the keyframe. - s(6) bit-width fix in vp9.c (4 mag + 1 sign -> 6 mag + 1 sign per VP9 spec) was a real bug too, latent because Bug 1 (this commit's fix) prevented its code path from running. Both fixes ship together. Pixels still produce 0x4c constant pattern post-fix — that is Bug 2 (substrate-wide cap_pool readback regression on linux-fresnel-fourier 7.0-1) per phase7_iter4_verification.md. Bug 2 is out of iter4 scope per Option-A choice; transitive proof remains the criterion-4 verification path. 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.