test0r
841f616e74
VAAPI signals "explicit scaling lists are present in the bitstream"
implicitly: the consumer (ffmpeg-vaapi, mpv, etc.) sends a
VAIQMatrixBufferH264 alongside RenderPicture iff
sps_scaling_matrix_present_flag || pps_scaling_matrix_present_flag.
When the bitstream uses default (flat) scaling, no IQMatrixBuffer
arrives and the in-tree h264.matrix struct stays zero-initialised.
fourier's existing codec_store_buffer for MPEG2 and HEVC tracks this
via a per-surface iqmatrix_set boolean (surface.h::mpeg2.iqmatrix_set,
h265.iqmatrix_set) — the H.264 path was missing the equivalent flag,
so set_controls always submitted the scaling matrix, including the
zero-initialised case.
Symptom on hantro-vpu RK3568: when TRANSFORM_8X8_MODE is enabled in
PPS, the kernel multiplies all 8x8 DCT coefficients by the zeroed
scaling_list_8x8, producing a zeroed CAPTURE buffer despite a
successful decode round-trip (no V4L2_BUF_FLAG_ERROR,
bytesused=3655712 reported).
Earlier draft of this patch unconditionally omitted SCALING_MATRIX in
FRAME_BASED. That's corpus-correct (bbb has no explicit scaling
lists) but the wrong predicate: the kernel-side gating is by
"matrix-supplied vs. not," not by decode mode. Streams that signal
explicit scaling lists must submit SCALING_MATRIX in either mode.
Contract verification (audit_0008_decode_params_2026-05-01.md +
hantro_h264.c::assemble_scaling_list): the kernel uses the supplied
matrix when SCALING_MATRIX is in the control batch and falls back
to spec-defined defaults when absent. Mode-independent.
This patch:
- surface.h: adds bool matrix_set to params.h264, mirroring
mpeg2.iqmatrix_set / h265.iqmatrix_set.
- picture.c codec_store_buffer (H.264 VAIQMatrixBufferType case):
sets matrix_set = true when the buffer arrives.
- picture.c RequestBeginPicture: resets matrix_set = false at the
start of each Begin/Render/End cycle.
- h264.c h264_set_controls: builds the controls[] array
incrementally; SPS/PPS/DECODE_PARAMS always; SCALING_MATRIX iff
matrix_set; SLICE_PARAMS only in SLICE_BASED; PRED_WEIGHTS only
when both SLICE_BASED and V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED.
The pre-existing FRAME_BASED-omits-SLICE_PARAMS rule is preserved —
kernel doc ext-ctrls-codec-stateless.rst:752: "When this mode is
selected, the V4L2_CID_STATELESS_H264_SLICE_PARAMS control shall
not be set."
Cross-reference: kernel UAPI section
ext-ctrls-codec-stateless.rst V4L2_CID_STATELESS_H264_SCALING_MATRIX
(matrix supplied iff explicit scaling lists in bitstream) and
hantro_h264.c::assemble_scaling_list (consumes supplied matrix or
falls back to defaults).
Signed-off-by: Markus Fritsche <fritsche.markus@gmail.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.