test0r
d41a4b96b3
Three Tier-2C/1B fixes from diff_against_ffmpeg.md (campaign repo): 1. Submit V4L2_CID_STATELESS_H264_SCALING_MATRIX every frame, with the H.264 spec flat default (every entry = 16) when the consumer didn't send a VAIQMatrixBufferH264. New helper: h264_default_flat_scaling_matrix(). Mirrors FFmpeg's v4l2_request_h264.c which always provides a scaling matrix. Replaces patch 0012's VAIQMatrixBuffer-conditional submission — that was corpus-correct (bbb has no explicit scaling lists) but inconsistent with what hantro G1 expects. 2. Set pps->flags |= V4L2_H264_PPS_FLAG_SCALING_MATRIX_PRESENT unconditionally. Hantro G1's set_params reads this flag to gate G1_REG_DEC_CTRL2_TYPE1_QUANT_E. 3. Populate pps->num_ref_idx_l0/l1_default_active_minus1 from VASliceParameterBufferH264.num_ref_idx_l*_active_minus1. Hantro G1 writes both into G1_REG_DEC_CTRL6_REFIDX0_ACTIVE / REFIDX1_ACTIVE. VAAPI doesn't expose the parsed-PPS default fields; the per-slice override is the closest available source (matches PPS default except on streams with explicit per-slice override). Why now: 2026-05-04 Phase 0 kernel-side audit (kernel source drivers/media/platform/verisilicon/hantro_g1_h264_dec.c) showed hantro G1 writes these fields directly into hardware MMIO registers. Prior assumption that they're "informational" or that "VAAPI handles defaults" was wrong — the hardware uses them to bit-walk the slice header and to size reference lists. See ~/src/libva-multiplanar/diff_against_ffmpeg.md. This is the easy half of the fix. The load-bearing half — adding a slice-header bit-parser to populate dec_param->dec_ref_pic_ marking_bit_size, idr_pic_id, pic_order_cnt_bit_size — comes in the 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.